Index: CMakeLists.txt
===================================================================
--- CMakeLists.txt
+++ CMakeLists.txt
@@ -193,8 +193,15 @@
 if (NOT(CLANG_DEFAULT_CXX_STDLIB STREQUAL "" OR
         CLANG_DEFAULT_CXX_STDLIB STREQUAL "libstdc++" OR
         CLANG_DEFAULT_CXX_STDLIB STREQUAL "libc++"))
-  message(WARNING "Resetting default C++ stdlib to use architecture default")
-  set(CLANG_DEFAULT_CXX_STDLIB "")
+  message(FATAL_ERROR "Invalid value for CLANG_DEFAULT_CXX_STDLIB")
+endif()
+
+set(CLANG_DEFAULT_RTLIB "" CACHE STRING
+  "Default runtime library to use (\"libgcc\" or \"compiler-rt\", empty for platform default)")
+if (NOT(CLANG_DEFAULT_RTLIB STREQUAL "" OR
+        CLANG_DEFAULT_RTLIB STREQUAL "libgcc" OR
+        CLANG_DEFAULT_RTLIB STREQUAL "compiler-rt"))
+  message(FATAL_ERROR "Invalid value for CLANG_DEFAULT_RTLIB")
 endif()
 
 set(CLANG_DEFAULT_OPENMP_RUNTIME "libomp" CACHE STRING
Index: include/clang/Config/config.h.cmake
===================================================================
--- include/clang/Config/config.h.cmake
+++ include/clang/Config/config.h.cmake
@@ -11,6 +11,9 @@
 /* Default C++ stdlib to use. */
 #define CLANG_DEFAULT_CXX_STDLIB "${CLANG_DEFAULT_CXX_STDLIB}"
 
+/* Default runtime library to use. */
+#define CLANG_DEFAULT_RTLIB "${CLANG_DEFAULT_RTLIB}"
+
 /* Default OpenMP runtime used by -fopenmp. */
 #define CLANG_DEFAULT_OPENMP_RUNTIME "${CLANG_DEFAULT_OPENMP_RUNTIME}"
 
Index: lib/Driver/ToolChain.cpp
===================================================================
--- lib/Driver/ToolChain.cpp
+++ lib/Driver/ToolChain.cpp
@@ -527,15 +527,19 @@
 
 ToolChain::RuntimeLibType ToolChain::GetRuntimeLibType(
     const ArgList &Args) const {
-  if (Arg *A = Args.getLastArg(options::OPT_rtlib_EQ)) {
-    StringRef Value = A->getValue();
-    if (Value == "compiler-rt")
-      return ToolChain::RLT_CompilerRT;
-    if (Value == "libgcc")
-      return ToolChain::RLT_Libgcc;
-    getDriver().Diag(diag::err_drv_invalid_rtlib_name)
-      << A->getAsString(Args);
-  }
+  const Arg* A = Args.getLastArg(options::OPT_rtlib_EQ);
+  StringRef LibName = A ? A->getValue() : CLANG_DEFAULT_RTLIB;
+
+  // "platform" is only used in tests to override CLANG_DEFAULT_RTLIB
+  if (LibName == "compiler-rt")
+    return ToolChain::RLT_CompilerRT;
+  else if (LibName == "libgcc")
+    return ToolChain::RLT_Libgcc;
+  else if (LibName == "platform")
+    return GetDefaultRuntimeLibType();
+
+  if (A)
+    getDriver().Diag(diag::err_drv_invalid_rtlib_name) << A->getAsString(Args);
 
   return GetDefaultRuntimeLibType();
 }
Index: test/Driver/linux-ld.c
===================================================================
--- test/Driver/linux-ld.c
+++ test/Driver/linux-ld.c
@@ -16,7 +16,7 @@
 // CHECK-LD-32: "-L[[SYSROOT]]/usr/lib"
 //
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
-// RUN:     --target=x86_64-unknown-linux \
+// RUN:     --target=x86_64-unknown-linux -rtlib=platform \
 // RUN:     --gcc-toolchain="" \
 // RUN:     --sysroot=%S/Inputs/basic_linux_tree \
 // RUN:   | FileCheck --check-prefix=CHECK-LD-64 %s
@@ -36,7 +36,7 @@
 // CHECK-LD-64: "-lgcc" "--as-needed" "-lgcc_s" "--no-as-needed"
 //
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
-// RUN:     --target=x86_64-unknown-linux-gnux32 \
+// RUN:     --target=x86_64-unknown-linux-gnux32 -rtlib=platform \
 // RUN:     --gcc-toolchain="" \
 // RUN:     --sysroot=%S/Inputs/basic_linux_tree \
 // RUN:   | FileCheck --check-prefix=CHECK-LD-X32 %s
@@ -86,7 +86,7 @@
 // CHECK-LD-RT-ANDROID: libclang_rt.builtins-arm-android.a"
 //
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
-// RUN:     --target=x86_64-unknown-linux \
+// RUN:     --target=x86_64-unknown-linux -rtlib=platform \
 // RUN:     --gcc-toolchain="" \
 // RUN:     --sysroot=%S/Inputs/basic_linux_tree \
 // RUN:     --rtlib=libgcc \
@@ -107,7 +107,7 @@
 // CHECK-LD-GCC: "-lgcc" "--as-needed" "-lgcc_s" "--no-as-needed"
 //
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
-// RUN:     --target=x86_64-unknown-linux \
+// RUN:     --target=x86_64-unknown-linux -rtlib=platform \
 // RUN:     -static-libgcc \
 // RUN:     --gcc-toolchain="" \
 // RUN:     --sysroot=%S/Inputs/basic_linux_tree \
@@ -128,7 +128,7 @@
 // CHECK-LD-64-STATIC-LIBGCC: "-lgcc" "-lgcc_eh"
 //
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
-// RUN:     --target=x86_64-unknown-linux \
+// RUN:     --target=x86_64-unknown-linux -rtlib=platform \
 // RUN:     -static \
 // RUN:     --gcc-toolchain="" \
 // RUN:     --sysroot=%S/Inputs/basic_linux_tree \
@@ -149,7 +149,7 @@
 //
 // Check that flags can be combined. The -static dominates.
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
-// RUN:     --target=x86_64-unknown-linux \
+// RUN:     --target=x86_64-unknown-linux -rtlib=platform \
 // RUN:     -static-libgcc -static \
 // RUN:     --gcc-toolchain="" \
 // RUN:     --sysroot=%S/Inputs/basic_linux_tree \
@@ -1004,42 +1004,42 @@
 //
 // Test linker invocation on Android.
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
-// RUN:     --target=arm-linux-androideabi \
+// RUN:     --target=arm-linux-androideabi -rtlib=platform \
 // RUN:     --gcc-toolchain="" \
 // RUN:     --sysroot=%S/Inputs/basic_android_tree/sysroot \
 // RUN:   | FileCheck --check-prefix=CHECK-ANDROID %s
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
-// RUN:     --target=arm-linux-android \
+// RUN:     --target=arm-linux-android -rtlib=platform \
 // RUN:     --gcc-toolchain="" \
 // RUN:     --sysroot=%S/Inputs/basic_android_tree/sysroot \
 // RUN:   | FileCheck --check-prefix=CHECK-ANDROID %s
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
-// RUN:     --target=aarch64-linux-android \
+// RUN:     --target=aarch64-linux-android -rtlib=platform \
 // RUN:     --gcc-toolchain="" \
 // RUN:     --sysroot=%S/Inputs/basic_android_tree/sysroot \
 // RUN:   | FileCheck --check-prefix=CHECK-ANDROID %s
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
-// RUN:     --target=arm64-linux-android \
+// RUN:     --target=arm64-linux-android -rtlib=platform \
 // RUN:     --gcc-toolchain="" \
 // RUN:     --sysroot=%S/Inputs/basic_android_tree/sysroot \
 // RUN:   | FileCheck --check-prefix=CHECK-ANDROID %s
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
-// RUN:     --target=mipsel-linux-android \
+// RUN:     --target=mipsel-linux-android -rtlib=platform \
 // RUN:     --gcc-toolchain="" \
 // RUN:     --sysroot=%S/Inputs/basic_android_tree/sysroot \
 // RUN:   | FileCheck --check-prefix=CHECK-ANDROID %s
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
-// RUN:     --target=mips64el-linux-android \
+// RUN:     --target=mips64el-linux-android -rtlib=platform \
 // RUN:     --gcc-toolchain="" \
 // RUN:     --sysroot=%S/Inputs/basic_android_tree/sysroot \
 // RUN:   | FileCheck --check-prefix=CHECK-ANDROID %s
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
-// RUN:     --target=i686-linux-android \
+// RUN:     --target=i686-linux-android -rtlib=platform \
 // RUN:     --gcc-toolchain="" \
 // RUN:     --sysroot=%S/Inputs/basic_android_tree/sysroot \
 // RUN:   | FileCheck --check-prefix=CHECK-ANDROID %s
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
-// RUN:     --target=x86_64-linux-android \
+// RUN:     --target=x86_64-linux-android -rtlib=platform \
 // RUN:     --gcc-toolchain="" \
 // RUN:     --sysroot=%S/Inputs/basic_android_tree/sysroot \
 // RUN:   | FileCheck --check-prefix=CHECK-ANDROID %s
@@ -1052,48 +1052,48 @@
 // CHECK-ANDROID-NOT: "gcc_s"
 // CHECK-ANDROID: "{{.*}}{{/|\\\\}}crtend_android.o"
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
-// RUN:     --target=arm-linux-androideabi \
+// RUN:     --target=arm-linux-androideabi -rtlib=platform \
 // RUN:     --gcc-toolchain="" \
 // RUN:     --sysroot=%S/Inputs/basic_android_tree/sysroot \
 // RUN:     -shared \
 // RUN:   | FileCheck --check-prefix=CHECK-ANDROID-SO %s
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
-// RUN:     --target=arm-linux-android \
+// RUN:     --target=arm-linux-android -rtlib=platform \
 // RUN:     --gcc-toolchain="" \
 // RUN:     --sysroot=%S/Inputs/basic_android_tree/sysroot \
 // RUN:     -shared \
 // RUN:   | FileCheck --check-prefix=CHECK-ANDROID-SO %s
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
-// RUN:     --target=aarch64-linux-android \
+// RUN:     --target=aarch64-linux-android -rtlib=platform \
 // RUN:     --gcc-toolchain="" \
 // RUN:     --sysroot=%S/Inputs/basic_android_tree/sysroot \
 // RUN:     -shared \
 // RUN:   | FileCheck --check-prefix=CHECK-ANDROID-SO %s
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
-// RUN:     --target=arm64-linux-android \
+// RUN:     --target=arm64-linux-android -rtlib=platform \
 // RUN:     --sysroot=%S/Inputs/basic_android_tree/sysroot \
 // RUN:     -shared \
 // RUN:   | FileCheck --check-prefix=CHECK-ANDROID-SO %s
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
-// RUN:     --target=mipsel-linux-android \
+// RUN:     --target=mipsel-linux-android -rtlib=platform \
 // RUN:     --gcc-toolchain="" \
 // RUN:     --sysroot=%S/Inputs/basic_android_tree/sysroot \
 // RUN:     -shared \
 // RUN:   | FileCheck --check-prefix=CHECK-ANDROID-SO %s
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
-// RUN:     --target=mips64el-linux-android \
+// RUN:     --target=mips64el-linux-android -rtlib=platform \
 // RUN:     --gcc-toolchain="" \
 // RUN:     --sysroot=%S/Inputs/basic_android_tree/sysroot \
 // RUN:     -shared \
 // RUN:   | FileCheck --check-prefix=CHECK-ANDROID-SO %s
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
-// RUN:     --target=i686-linux-android \
+// RUN:     --target=i686-linux-android -rtlib=platform \
 // RUN:     --gcc-toolchain="" \
 // RUN:     --sysroot=%S/Inputs/basic_android_tree/sysroot \
 // RUN:     -shared \
 // RUN:   | FileCheck --check-prefix=CHECK-ANDROID-SO %s
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
-// RUN:     --target=x86_64-linux-android \
+// RUN:     --target=x86_64-linux-android -rtlib=platform \
 // RUN:     --gcc-toolchain="" \
 // RUN:     --sysroot=%S/Inputs/basic_android_tree/sysroot \
 // RUN:     -shared \
@@ -1108,47 +1108,47 @@
 // CHECK-ANDROID-SO-NOT: "gcc_s"
 // CHECK-ANDROID-SO: "{{.*}}{{/|\\\\}}crtend_so.o"
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
-// RUN:     --target=arm-linux-androideabi \
+// RUN:     --target=arm-linux-androideabi -rtlib=platform \
 // RUN:     --gcc-toolchain="" \
 // RUN:     --sysroot=%S/Inputs/basic_android_tree/sysroot \
 // RUN:     -static \
 // RUN:   | FileCheck --check-prefix=CHECK-ANDROID-STATIC %s
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
-// RUN:     --target=arm-linux-android \
+// RUN:     --target=arm-linux-android -rtlib=platform \
 // RUN:     --sysroot=%S/Inputs/basic_android_tree/sysroot \
 // RUN:     -static \
 // RUN:   | FileCheck --check-prefix=CHECK-ANDROID-STATIC %s
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
-// RUN:     --target=aarch64-linux-android \
+// RUN:     --target=aarch64-linux-android -rtlib=platform \
 // RUN:     --gcc-toolchain="" \
 // RUN:     --sysroot=%S/Inputs/basic_android_tree/sysroot \
 // RUN:     -static \
 // RUN:   | FileCheck --check-prefix=CHECK-ANDROID-STATIC %s
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
-// RUN:     --target=arm64-linux-android \
+// RUN:     --target=arm64-linux-android -rtlib=platform \
 // RUN:     --sysroot=%S/Inputs/basic_android_tree/sysroot \
 // RUN:     -static \
 // RUN:   | FileCheck --check-prefix=CHECK-ANDROID-STATIC %s
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
-// RUN:     --target=mipsel-linux-android \
+// RUN:     --target=mipsel-linux-android -rtlib=platform \
 // RUN:     --gcc-toolchain="" \
 // RUN:     --sysroot=%S/Inputs/basic_android_tree/sysroot \
 // RUN:     -static \
 // RUN:   | FileCheck --check-prefix=CHECK-ANDROID-STATIC %s
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
-// RUN:     --target=mips64el-linux-android \
+// RUN:     --target=mips64el-linux-android -rtlib=platform \
 // RUN:     --gcc-toolchain="" \
 // RUN:     --sysroot=%S/Inputs/basic_android_tree/sysroot \
 // RUN:     -static \
 // RUN:   | FileCheck --check-prefix=CHECK-ANDROID-STATIC %s
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
-// RUN:     --target=i686-linux-android \
+// RUN:     --target=i686-linux-android -rtlib=platform \
 // RUN:     --gcc-toolchain="" \
 // RUN:     --sysroot=%S/Inputs/basic_android_tree/sysroot \
 // RUN:     -static \
 // RUN:   | FileCheck --check-prefix=CHECK-ANDROID-STATIC %s
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
-// RUN:     --target=x86_64-linux-android \
+// RUN:     --target=x86_64-linux-android -rtlib=platform \
 // RUN:     --gcc-toolchain="" \
 // RUN:     --sysroot=%S/Inputs/basic_android_tree/sysroot \
 // RUN:     -static \
@@ -1162,49 +1162,49 @@
 // CHECK-ANDROID-STATIC-NOT: "gcc_s"
 // CHECK-ANDROID-STATIC: "{{.*}}{{/|\\\\}}crtend_android.o"
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
-// RUN:     --target=arm-linux-androideabi \
+// RUN:     --target=arm-linux-androideabi -rtlib=platform \
 // RUN:     --gcc-toolchain="" \
 // RUN:     --sysroot=%S/Inputs/basic_android_tree/sysroot  \
 // RUN:     -pie \
 // RUN:   | FileCheck --check-prefix=CHECK-ANDROID-PIE %s
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
-// RUN:     --target=arm-linux-android \
+// RUN:     --target=arm-linux-android -rtlib=platform \
 // RUN:     --gcc-toolchain="" \
 // RUN:     --sysroot=%S/Inputs/basic_android_tree/sysroot \
 // RUN:     -pie \
 // RUN:   | FileCheck --check-prefix=CHECK-ANDROID-PIE %s
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
-// RUN:     --target=aarch64-linux-android \
+// RUN:     --target=aarch64-linux-android -rtlib=platform \
 // RUN:     --gcc-toolchain="" \
 // RUN:     --sysroot=%S/Inputs/basic_android_tree/sysroot  \
 // RUN:     -pie \
 // RUN:   | FileCheck --check-prefix=CHECK-ANDROID-PIE %s
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
-// RUN:     --target=arm64-linux-android \
+// RUN:     --target=arm64-linux-android -rtlib=platform \
 // RUN:     --gcc-toolchain="" \
 // RUN:     --sysroot=%S/Inputs/basic_android_tree/sysroot  \
 // RUN:     -pie \
 // RUN:   | FileCheck --check-prefix=CHECK-ANDROID-PIE %s
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
-// RUN:     --target=mipsel-linux-android \
+// RUN:     --target=mipsel-linux-android -rtlib=platform \
 // RUN:     --gcc-toolchain="" \
 // RUN:     --sysroot=%S/Inputs/basic_android_tree/sysroot \
 // RUN:     -pie \
 // RUN:   | FileCheck --check-prefix=CHECK-ANDROID-PIE %s
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
-// RUN:     --target=mips64el-linux-android \
+// RUN:     --target=mips64el-linux-android -rtlib=platform \
 // RUN:     --gcc-toolchain="" \
 // RUN:     --sysroot=%S/Inputs/basic_android_tree/sysroot \
 // RUN:     -pie \
 // RUN:   | FileCheck --check-prefix=CHECK-ANDROID-PIE %s
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
-// RUN:     --target=i686-linux-android \
+// RUN:     --target=i686-linux-android -rtlib=platform \
 // RUN:     --gcc-toolchain="" \
 // RUN:     --sysroot=%S/Inputs/basic_android_tree/sysroot \
 // RUN:     -pie \
 // RUN:   | FileCheck --check-prefix=CHECK-ANDROID-PIE %s
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
-// RUN:     --target=x86_64-linux-android \
+// RUN:     --target=x86_64-linux-android -rtlib=platform \
 // RUN:     --gcc-toolchain="" \
 // RUN:     --sysroot=%S/Inputs/basic_android_tree/sysroot \
 // RUN:     -pie \
Index: test/Driver/miamcu-opt.c
===================================================================
--- test/Driver/miamcu-opt.c
+++ test/Driver/miamcu-opt.c
@@ -1,13 +1,13 @@
 // REQUIRES: clang-driver
 // REQUIRES: x86-registered-target
 //
-// RUN: %clang -miamcu -no-canonical-prefixes %s -### -o %t.o 2>&1 | FileCheck %s
-// RUN: %clang -miamcu -no-canonical-prefixes -m32 %s -### -o %t.o 2>&1 | FileCheck %s
-// RUN: %clang -miamcu -no-canonical-prefixes -target x86_64-unknown-linux-gnu %s -### -o %t.o 2>&1 | FileCheck %s
-// RUN: %clang -mno-iamcu -miamcu -no-canonical-prefixes %s -### -o %t.o 2>&1 | FileCheck %s
-// RUN: %clang -miamcu -no-canonical-prefixes -m64 %s -### -o %t.o 2>&1 | FileCheck %s -check-prefix=M64
-// RUN: %clang -miamcu -no-canonical-prefixes -dynamic %s -### -o %t.o 2>&1 | FileCheck %s -check-prefix=DYNAMIC
-// RUN: %clang -miamcu -no-canonical-prefixes  -target armv8-eabi %s -### -o %t.o 2>&1 | FileCheck %s -check-prefix=NOT-X86
+// RUN: %clang -miamcu -rtlib=platform -no-canonical-prefixes %s -### -o %t.o 2>&1 | FileCheck %s
+// RUN: %clang -miamcu -rtlib=platform -no-canonical-prefixes -m32 %s -### -o %t.o 2>&1 | FileCheck %s
+// RUN: %clang -miamcu -rtlib=platform -no-canonical-prefixes -target x86_64-unknown-linux-gnu %s -### -o %t.o 2>&1 | FileCheck %s
+// RUN: %clang -mno-iamcu -miamcu -rtlib=platform -no-canonical-prefixes %s -### -o %t.o 2>&1 | FileCheck %s
+// RUN: %clang -miamcu -rtlib=platform -no-canonical-prefixes -m64 %s -### -o %t.o 2>&1 | FileCheck %s -check-prefix=M64
+// RUN: %clang -miamcu -rtlib=platform -no-canonical-prefixes -dynamic %s -### -o %t.o 2>&1 | FileCheck %s -check-prefix=DYNAMIC
+// RUN: %clang -miamcu -rtlib=platform -no-canonical-prefixes  -target armv8-eabi %s -### -o %t.o 2>&1 | FileCheck %s -check-prefix=NOT-X86
 // RUN: %clang -miamcu -mno-iamcu -no-canonical-prefixes -target x86_64-unknown-linux-gnu %s -### -o %t.o 2>&1 | FileCheck %s -check-prefix=MNOIAMCU
 
 // M64: error: invalid argument '-miamcu' not allowed with '-m64'
Index: test/Driver/miamcu-opt.cpp
===================================================================
--- test/Driver/miamcu-opt.cpp
+++ test/Driver/miamcu-opt.cpp
@@ -1,3 +1,3 @@
-// RUN: %clang -miamcu %s -### -o %t.o 2>&1 | FileCheck %s
+// RUN: %clang -miamcu -rtlib=platform %s -### -o %t.o 2>&1 | FileCheck %s
 
 // CHECK: error: the clang compiler does not support 'C++ for IAMCU'
Index: test/Driver/mingw-libgcc.c
===================================================================
--- test/Driver/mingw-libgcc.c
+++ test/Driver/mingw-libgcc.c
@@ -2,24 +2,24 @@
 // Verified with gcc version 5.1.0 (i686-posix-dwarf-rev0, Built by MinGW-W64 project).
 
 // gcc, static
-// RUN: %clang -v -target i686-pc-windows-gnu -### %s 2>&1 | FileCheck -check-prefix=CHECK_STATIC %s
-// RUN: %clang -static -v -target i686-pc-windows-gnu -### %s 2>&1 | FileCheck -check-prefix=CHECK_STATIC %s
-// RUN: %clang -static-libgcc -v -target i686-pc-windows-gnu -### %s 2>&1 | FileCheck -check-prefix=CHECK_STATIC %s
-// RUN: %clang -static -shared -v -target i686-pc-windows-gnu -### %s 2>&1 | FileCheck -check-prefix=CHECK_STATIC %s
-// RUN: %clang -static-libgcc -shared -v -target i686-pc-windows-gnu -### %s 2>&1 | FileCheck -check-prefix=CHECK_STATIC %s
+// RUN: %clang -v -target i686-pc-windows-gnu -rtlib=platform -### %s 2>&1 | FileCheck -check-prefix=CHECK_STATIC %s
+// RUN: %clang -static -v -target i686-pc-windows-gnu -rtlib=platform -### %s 2>&1 | FileCheck -check-prefix=CHECK_STATIC %s
+// RUN: %clang -static-libgcc -v -target i686-pc-windows-gnu -rtlib=platform -### %s 2>&1 | FileCheck -check-prefix=CHECK_STATIC %s
+// RUN: %clang -static -shared -v -target i686-pc-windows-gnu -rtlib=platform -### %s 2>&1 | FileCheck -check-prefix=CHECK_STATIC %s
+// RUN: %clang -static-libgcc -shared -v -target i686-pc-windows-gnu -rtlib=platform -### %s 2>&1 | FileCheck -check-prefix=CHECK_STATIC %s
 
 // gcc, dynamic
-// RUN: %clang -shared -v -target i686-pc-windows-gnu -### %s 2>&1 | FileCheck -check-prefix=CHECK_DYNAMIC %s
+// RUN: %clang -shared -v -target i686-pc-windows-gnu -rtlib=platform -### %s 2>&1 | FileCheck -check-prefix=CHECK_DYNAMIC %s
 
 // g++, static
-// RUN: %clang -static --driver-mode=g++ -v -target i686-pc-windows-gnu -### %s 2>&1 | FileCheck -check-prefix=CHECK_STATIC %s
-// RUN: %clang -static-libgcc --driver-mode=g++ -v -target i686-pc-windows-gnu -### %s 2>&1 | FileCheck -check-prefix=CHECK_STATIC %s
-// RUN: %clang -static -shared --driver-mode=g++ -v -target i686-pc-windows-gnu -### %s 2>&1 | FileCheck -check-prefix=CHECK_STATIC %s
-// RUN: %clang -static-libgcc -shared --driver-mode=g++ -v -target i686-pc-windows-gnu -### %s 2>&1 | FileCheck -check-prefix=CHECK_STATIC %s
+// RUN: %clang -static --driver-mode=g++ -v -target i686-pc-windows-gnu -rtlib=platform -### %s 2>&1 | FileCheck -check-prefix=CHECK_STATIC %s
+// RUN: %clang -static-libgcc --driver-mode=g++ -v -target i686-pc-windows-gnu -rtlib=platform -### %s 2>&1 | FileCheck -check-prefix=CHECK_STATIC %s
+// RUN: %clang -static -shared --driver-mode=g++ -v -target i686-pc-windows-gnu -rtlib=platform -### %s 2>&1 | FileCheck -check-prefix=CHECK_STATIC %s
+// RUN: %clang -static-libgcc -shared --driver-mode=g++ -v -target i686-pc-windows-gnu -rtlib=platform -### %s 2>&1 | FileCheck -check-prefix=CHECK_STATIC %s
 
 // g++, dynamic
-// RUN: %clang --driver-mode=g++ -v -target i686-pc-windows-gnu -### %s 2>&1 | FileCheck -check-prefix=CHECK_DYNAMIC %s
-// RUN: %clang -shared --driver-mode=g++ -v -target i686-pc-windows-gnu -### %s 2>&1 | FileCheck -check-prefix=CHECK_DYNAMIC %s
+// RUN: %clang --driver-mode=g++ -v -target i686-pc-windows-gnu -rtlib=platform -### %s 2>&1 | FileCheck -check-prefix=CHECK_DYNAMIC %s
+// RUN: %clang -shared --driver-mode=g++ -v -target i686-pc-windows-gnu -rtlib=platform -### %s 2>&1 | FileCheck -check-prefix=CHECK_DYNAMIC %s
 
 // CHECK_STATIC: "-lgcc" "-lgcc_eh"
 // CHECK_DYNAMIC: "-lgcc_s" "-lgcc"
Index: test/Driver/mingw.cpp
===================================================================
--- test/Driver/mingw.cpp
+++ test/Driver/mingw.cpp
@@ -1,9 +1,9 @@
-// RUN: %clang -target i686-windows-gnu -c -### --sysroot=%S/Inputs/mingw_clang_tree/mingw32 %s 2>&1 | FileCheck -check-prefix=CHECK_MINGW_CLANG_TREE %s
+// RUN: %clang -target i686-windows-gnu -rtlib=platform -c -### --sysroot=%S/Inputs/mingw_clang_tree/mingw32 %s 2>&1 | FileCheck -check-prefix=CHECK_MINGW_CLANG_TREE %s
 // CHECK_MINGW_CLANG_TREE: "{{.*}}/Inputs/mingw_clang_tree/mingw32{{/|\\\\}}i686-w64-mingw32{{/|\\\\}}include"
 // CHECK_MINGW_CLANG_TREE: "{{.*}}/Inputs/mingw_clang_tree/mingw32{{/|\\\\}}include"
 
 
-// RUN: %clang -target i686-pc-windows-gnu -stdlib=libstdc++ -c -### --sysroot=%S/Inputs/mingw_mingw_org_tree/mingw %s 2>&1 | FileCheck -check-prefix=CHECK_MINGW_ORG_TREE %s
+// RUN: %clang -target i686-pc-windows-gnu -rtlib=platform -stdlib=libstdc++ -c -### --sysroot=%S/Inputs/mingw_mingw_org_tree/mingw %s 2>&1 | FileCheck -check-prefix=CHECK_MINGW_ORG_TREE %s
 // CHECK_MINGW_ORG_TREE: "{{.*}}/Inputs/mingw_mingw_org_tree/mingw{{/|\\\\}}lib{{/|\\\\}}gcc{{/|\\\\}}mingw32{{/|\\\\}}4.8.1{{/|\\\\}}include{{/|\\\\}}c++"
 // CHECK_MINGW_ORG_TREE: "{{.*}}/Inputs/mingw_mingw_org_tree/mingw{{/|\\\\}}lib{{/|\\\\}}gcc{{/|\\\\}}mingw32{{/|\\\\}}4.8.1{{/|\\\\}}include{{/|\\\\}}c++{{/|\\\\}}mingw32"
 // CHECK_MINGW_ORG_TREE: "{{.*}}{{/|\\\\}}Inputs/mingw_mingw_org_tree/mingw{{/|\\\\}}lib{{/|\\\\}}gcc{{/|\\\\}}mingw32{{/|\\\\}}4.8.1{{/|\\\\}}include{{/|\\\\}}c++{{/|\\\\}}backward"
@@ -13,7 +13,7 @@
 // CHECK_MINGW_ORG_TREE: {{.*}}/Inputs/mingw_mingw_org_tree/mingw{{/|\\\\}}include
 
 
-// RUN: %clang -target i686-pc-windows-gnu -stdlib=libstdc++ -c -### --sysroot=%S/Inputs/mingw_mingw_builds_tree/mingw32 %s 2>&1 | FileCheck -check-prefix=CHECK_MINGW_BUILDS_TREE %s
+// RUN: %clang -target i686-pc-windows-gnu -rtlib=platform -stdlib=libstdc++ -c -### --sysroot=%S/Inputs/mingw_mingw_builds_tree/mingw32 %s 2>&1 | FileCheck -check-prefix=CHECK_MINGW_BUILDS_TREE %s
 // CHECK_MINGW_BUILDS_TREE: "{{.*}}/Inputs/mingw_mingw_builds_tree/mingw32{{/|\\\\}}i686-w64-mingw32{{/|\\\\}}include{{/|\\\\}}c++"
 // CHECK_MINGW_BUILDS_TREE: "{{.*}}/Inputs/mingw_mingw_builds_tree/mingw32{{/|\\\\}}i686-w64-mingw32{{/|\\\\}}include{{/|\\\\}}c++{{/|\\\\}}i686-w64-mingw32"
 // CHECK_MINGW_BUILDS_TREE: "{{.*}}/Inputs/mingw_mingw_builds_tree/mingw32{{/|\\\\}}i686-w64-mingw32{{/|\\\\}}include{{/|\\\\}}c++{{/|\\\\}}backward"
@@ -22,7 +22,7 @@
 // CHECK_MINGW_BUILDS_TREE: "{{.*}}/Inputs/mingw_mingw_builds_tree/mingw32{{/|\\\\}}i686-w64-mingw32{{/|\\\\}}include"
 
 
-// RUN: %clang -target i686-pc-windows-gnu -stdlib=libstdc++ -c -### --sysroot=%S/Inputs/mingw_msys2_tree/msys64/mingw32 %s 2>&1 | FileCheck -check-prefix=CHECK_MINGW_MSYS_TREE %s
+// RUN: %clang -target i686-pc-windows-gnu -rtlib=platform -stdlib=libstdc++ -c -### --sysroot=%S/Inputs/mingw_msys2_tree/msys64/mingw32 %s 2>&1 | FileCheck -check-prefix=CHECK_MINGW_MSYS_TREE %s
 // CHECK_MINGW_MSYS_TREE: "{{.*}}/Inputs/mingw_msys2_tree/msys64{{/|\\\\}}mingw32{{/|\\\\}}include{{/|\\\\}}c++{{/|\\\\}}4.9.2"
 // CHECK_MINGW_MSYS_TREE: "{{.*}}/Inputs/mingw_msys2_tree/msys64/mingw32{{/|\\\\}}include{{/|\\\\}}c++{{/|\\\\}}4.9.2{{/|\\\\}}i686-w64-mingw32"
 // CHECK_MINGW_MSYS_TREE: "{{.*}}/Inputs/mingw_msys2_tree/msys64/mingw32{{/|\\\\}}include{{/|\\\\}}c++{{/|\\\\}}4.9.2{{/|\\\\}}backward"
@@ -32,7 +32,7 @@
 // CHECK_MINGW_MSYS_TREE: "{{.*}}/Inputs/mingw_msys2_tree/msys64/mingw32{{/|\\\\}}include"
 
 
-// RUN: %clang -target x86_64-pc-windows-gnu -stdlib=libstdc++ -c -### --sysroot=%S/Inputs/mingw_opensuse_tree/usr %s 2>&1 | FileCheck -check-prefix=CHECK_MINGW_OPENSUSE_TREE %s
+// RUN: %clang -target x86_64-pc-windows-gnu -rtlib=platform -stdlib=libstdc++ -c -### --sysroot=%S/Inputs/mingw_opensuse_tree/usr %s 2>&1 | FileCheck -check-prefix=CHECK_MINGW_OPENSUSE_TREE %s
 // CHECK_MINGW_OPENSUSE_TREE: "{{.*}}/Inputs/mingw_opensuse_tree/usr{{/|\\\\}}lib64{{/|\\\\}}gcc{{/|\\\\}}x86_64-w64-mingw32{{/|\\\\}}5.1.0{{/|\\\\}}include{{/|\\\\}}c++"
 // CHECK_MINGW_OPENSUSE_TREE: "{{.*}}/Inputs/mingw_opensuse_tree/usr{{/|\\\\}}lib64{{/|\\\\}}gcc{{/|\\\\}}x86_64-w64-mingw32{{/|\\\\}}5.1.0{{/|\\\\}}include{{/|\\\\}}c++{{/|\\\\}}x86_64-w64-mingw32"
 // CHECK_MINGW_OPENSUSE_TREE: "{{.*}}/Inputs/mingw_opensuse_tree/usr{{/|\\\\}}lib64{{/|\\\\}}gcc{{/|\\\\}}x86_64-w64-mingw32{{/|\\\\}}5.1.0{{/|\\\\}}include{{/|\\\\}}c++{{/|\\\\}}backward"
@@ -41,7 +41,7 @@
 // CHECK_MINGW_OPENSUSE_TREE: "{{.*}}/Inputs/mingw_opensuse_tree/usr{{/|\\\\}}lib64{{/|\\\\}}gcc{{/|\\\\}}x86_64-w64-mingw32{{/|\\\\}}5.1.0{{/|\\\\}}include-fixed"
 
 
-// RUN: %clang -target i686-pc-windows-gnu -stdlib=libstdc++ -c -### --sysroot=%S/Inputs/mingw_arch_tree/usr %s 2>&1 | FileCheck -check-prefix=CHECK_MINGW_ARCH_TREE %s
+// RUN: %clang -target i686-pc-windows-gnu -rtlib=platform -stdlib=libstdc++ -c -### --sysroot=%S/Inputs/mingw_arch_tree/usr %s 2>&1 | FileCheck -check-prefix=CHECK_MINGW_ARCH_TREE %s
 // CHECK_MINGW_ARCH_TREE: "{{.*}}/Inputs/mingw_arch_tree/usr{{/|\\\\}}i686-w64-mingw32{{/|\\\\}}include{{/|\\\\}}c++{{/|\\\\}}5.1.0"
 // CHECK_MINGW_ARCH_TREE: "{{.*}}/Inputs/mingw_arch_tree/usr{{/|\\\\}}i686-w64-mingw32{{/|\\\\}}include{{/|\\\\}}c++{{/|\\\\}}5.1.0{{/|\\\\}}i686-w64-mingw32"
 // CHECK_MINGW_ARCH_TREE: "{{.*}}/Inputs/mingw_arch_tree/usr{{/|\\\\}}i686-w64-mingw32{{/|\\\\}}include{{/|\\\\}}c++{{/|\\\\}}5.1.0{{/|\\\\}}backward"
@@ -50,7 +50,7 @@
 // CHECK_MINGW_ARCH_TREE: "{{.*}}/Inputs/mingw_arch_tree/usr{{/|\\\\}}i686-w64-mingw32{{/|\\\\}}include"
 
 
-// RUN: %clang -target x86_64-pc-windows-gnu -stdlib=libstdc++ -c -### --sysroot=%S/Inputs/mingw_ubuntu_tree/usr %s 2>&1 | FileCheck -check-prefix=CHECK_MINGW_UBUNTU_TREE %s
+// RUN: %clang -target x86_64-pc-windows-gnu -rtlib=platform -stdlib=libstdc++ -c -### --sysroot=%S/Inputs/mingw_ubuntu_tree/usr %s 2>&1 | FileCheck -check-prefix=CHECK_MINGW_UBUNTU_TREE %s
 // CHECK_MINGW_UBUNTU_TREE: "{{.*}}/Inputs/mingw_ubuntu_tree/usr{{/|\\\\}}include{{/|\\\\}}c++{{/|\\\\}}4.8"
 // CHECK_MINGW_UBUNTU_TREE: "{{.*}}/Inputs/mingw_ubuntu_tree/usr{{/|\\\\}}include{{/|\\\\}}c++{{/|\\\\}}4.8{{/|\\\\}}x86_64-w64-mingw32"
 // CHECK_MINGW_UBUNTU_TREE: "{{.*}}/Inputs/mingw_ubuntu_tree/usr{{/|\\\\}}include{{/|\\\\}}c++{{/|\\\\}}4.8{{/|\\\\}}backward"
Index: test/Driver/sanitizer-ld.c
===================================================================
--- test/Driver/sanitizer-ld.c
+++ test/Driver/sanitizer-ld.c
@@ -343,7 +343,7 @@
 
 // CFI by itself does not link runtime libraries.
 // RUN: %clang -fsanitize=cfi %s -### -o %t.o 2>&1 \
-// RUN:     -target x86_64-unknown-linux \
+// RUN:     -target x86_64-unknown-linux -rtlib=platform \
 // RUN:     --sysroot=%S/Inputs/basic_linux_tree \
 // RUN:   | FileCheck --check-prefix=CHECK-CFI-LINUX %s
 // CHECK-CFI-LINUX: "{{.*}}ld{{(.exe)?}}"
Index: test/Driver/windows-cross.c
===================================================================
--- test/Driver/windows-cross.c
+++ test/Driver/windows-cross.c
@@ -1,4 +1,4 @@
-// RUN: %clang -### -target armv7-windows-itanium --sysroot %S/Inputs/Windows/ARM/8.1 -B %S/Inputs/Windows/ARM/8.1/usr/bin -stdlib=libstdc++ -o /dev/null %s 2>&1 \
+// RUN: %clang -### -target armv7-windows-itanium --sysroot %S/Inputs/Windows/ARM/8.1 -B %S/Inputs/Windows/ARM/8.1/usr/bin -stdlib=libstdc++ -rtlib=platform -o /dev/null %s 2>&1 \
 // RUN:   | FileCheck %s --check-prefix CHECK-BASIC
 
 // CHECK-BASIC: armv7-windows-itanium-ld" "--sysroot={{.*}}/Inputs/Windows/ARM/8.1" "-m" "thumb2pe" "-Bdynamic" "--entry" "mainCRTStartup" "--allow-multiple-definition" "-o" "{{[^"]*}}" "{{.*}}/Inputs/Windows/ARM/8.1/usr/lib/crtbegin.obj" "-L{{.*}}/Inputs/Windows/ARM/8.1/usr/lib" "-L{{.*}}/Inputs/Windows/ARM/8.1/usr/lib/gcc" "{{.*}}.o" "-lmsvcrt" "-lgcc" "--as-needed" "-lgcc_s" "--no-as-needed"
Index: test/OpenMP/linking.c
===================================================================
--- test/OpenMP/linking.c
+++ test/OpenMP/linking.c
@@ -4,42 +4,42 @@
 // FIXME: Replace DEFAULT_OPENMP_LIB below with the value chosen at configure time.
 //
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
-// RUN:     -fopenmp -target i386-unknown-linux \
+// RUN:     -fopenmp -target i386-unknown-linux -rtlib=platform \
 // RUN:   | FileCheck --check-prefix=CHECK-LD-32 %s
 // CHECK-LD-32: "{{.*}}ld{{(.exe)?}}"
 // CHECK-LD-32: "-l[[DEFAULT_OPENMP_LIB:[^"]*]]" "-lgcc"
 // CHECK-LD-32: "-lpthread" "-lc"
 //
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
-// RUN:     -fopenmp -target x86_64-unknown-linux \
+// RUN:     -fopenmp -target x86_64-unknown-linux -rtlib=platform \
 // RUN:   | FileCheck --check-prefix=CHECK-LD-64 %s
 // CHECK-LD-64: "{{.*}}ld{{(.exe)?}}"
 // CHECK-LD-64: "-l[[DEFAULT_OPENMP_LIB:[^"]*]]" "-lgcc"
 // CHECK-LD-64: "-lpthread" "-lc"
 //
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
-// RUN:     -fopenmp=libgomp -target i386-unknown-linux \
+// RUN:     -fopenmp=libgomp -target i386-unknown-linux -rtlib=platform \
 // RUN:   | FileCheck --check-prefix=CHECK-GOMP-LD-32 %s
 // CHECK-GOMP-LD-32: "{{.*}}ld{{(.exe)?}}"
 // CHECK-GOMP-LD-32: "-lgomp" "-lrt" "-lgcc"
 // CHECK-GOMP-LD-32: "-lpthread" "-lc"
 //
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
-// RUN:     -fopenmp=libgomp -target x86_64-unknown-linux \
+// RUN:     -fopenmp=libgomp -target x86_64-unknown-linux -rtlib=platform \
 // RUN:   | FileCheck --check-prefix=CHECK-GOMP-LD-64 %s
 // CHECK-GOMP-LD-64: "{{.*}}ld{{(.exe)?}}"
 // CHECK-GOMP-LD-64: "-lgomp" "-lrt" "-lgcc"
 // CHECK-GOMP-LD-64: "-lpthread" "-lc"
 //
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
-// RUN:     -fopenmp -target i386-unknown-linux \
+// RUN:     -fopenmp -target i386-unknown-linux -rtlib=platform \
 // RUN:   | FileCheck --check-prefix=CHECK-IOMP5-LD-32 %s
 // CHECK-IOMP5-LD-32: "{{.*}}ld{{(.exe)?}}"
 // CHECK-IOMP5-LD-32: "-l[[DEFAULT_OPENMP_LIB:[^"]*]]" "-lgcc"
 // CHECK-IOMP5-LD-32: "-lpthread" "-lc"
 //
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
-// RUN:     -fopenmp -target x86_64-unknown-linux \
+// RUN:     -fopenmp -target x86_64-unknown-linux -rtlib=platform \
 // RUN:   | FileCheck --check-prefix=CHECK-IOMP5-LD-64 %s
 // CHECK-IOMP5-LD-64: "{{.*}}ld{{(.exe)?}}"
 // CHECK-IOMP5-LD-64: "-l[[DEFAULT_OPENMP_LIB:[^"]*]]" "-lgcc"
@@ -57,6 +57,7 @@
 //
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
 // RUN:     -fopenmp -fopenmp=libgomp -target i386-unknown-linux \
+// RUN:     -rtlib=platform \
 // RUN:   | FileCheck --check-prefix=CHECK-LD-OVERRIDE-32 %s
 // CHECK-LD-OVERRIDE-32: "{{.*}}ld{{(.exe)?}}"
 // CHECK-LD-OVERRIDE-32: "-lgomp" "-lrt" "-lgcc"
@@ -64,13 +65,14 @@
 //
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
 // RUN:     -fopenmp -fopenmp=libgomp -target x86_64-unknown-linux \
+// RUN:     -rtlib=platform \
 // RUN:   | FileCheck --check-prefix=CHECK-LD-OVERRIDE-64 %s
 // CHECK-LD-OVERRIDE-64: "{{.*}}ld{{(.exe)?}}"
 // CHECK-LD-OVERRIDE-64: "-lgomp" "-lrt" "-lgcc"
 // CHECK-LD-OVERRIDE-64: "-lpthread" "-lc"
 //
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
-// RUN:     -fopenmp=libomp -target x86_64-msvc-win32 \
+// RUN:     -fopenmp=libomp -target x86_64-msvc-win32 -rtlib=platform \
 // RUN:   | FileCheck --check-prefix=CHECK-MSVC-LINK-64 %s
 // CHECK-MSVC-LINK-64: link.exe
 // CHECK-MSVC-LINK-64-SAME: -nodefaultlib:vcomp.lib
@@ -79,7 +81,7 @@
 // CHECK-MSVC-LINK-64-SAME: -defaultlib:libomp.lib
 //
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
-// RUN:     -fopenmp=libiomp5 -target x86_64-msvc-win32 \
+// RUN:     -fopenmp=libiomp5 -target x86_64-msvc-win32 -rtlib=platform \
 // RUN:   | FileCheck --check-prefix=CHECK-MSVC-ILINK-64 %s
 // CHECK-MSVC-ILINK-64: link.exe
 // CHECK-MSVC-ILINK-64-SAME: -nodefaultlib:vcomp.lib