Index: compiler-rt/trunk/cmake/Modules/CompilerRTUtils.cmake
===================================================================
--- compiler-rt/trunk/cmake/Modules/CompilerRTUtils.cmake
+++ compiler-rt/trunk/cmake/Modules/CompilerRTUtils.cmake
@@ -100,6 +100,13 @@
   set(${out_var} ${archs} PARENT_SCOPE)
 endfunction()
 
+# Add $arch as supported with no additional flags.
+macro(add_default_target_arch arch)
+  set(TARGET_${arch}_CFLAGS "")
+  set(CAN_TARGET_${arch} 1)
+  list(APPEND COMPILER_RT_SUPPORTED_ARCH ${arch})
+endmacro()
+
 function(check_compile_definition def argstring out_var)
   if("${def}" STREQUAL "")
     set(${out_var} TRUE PARENT_SCOPE)
@@ -223,8 +230,16 @@
 endmacro()
 
 macro(construct_compiler_rt_default_triple)
-  set(COMPILER_RT_DEFAULT_TARGET_TRIPLE ${TARGET_TRIPLE} CACHE STRING
-      "Default triple for which compiler-rt runtimes will be built.")
+  if(COMPILER_RT_DEFAULT_TARGET_ONLY)
+    if(DEFINED COMPILER_RT_DEFAULT_TARGET_TRIPLE)
+      message(FATAL_ERROR "COMPILER_RT_DEFAULT_TARGET_TRIPLE isn't supported when building for default target only")
+    endif()
+    set(COMPILER_RT_DEFAULT_TARGET_TRIPLE ${CMAKE_C_COMPILER_TARGET})
+  else()
+    set(COMPILER_RT_DEFAULT_TARGET_TRIPLE ${TARGET_TRIPLE} CACHE STRING
+          "Default triple for which compiler-rt runtimes will be built.")
+  endif()
+
   if(DEFINED COMPILER_RT_TEST_TARGET_TRIPLE)
     # Backwards compatibility: this variable used to be called
     # COMPILER_RT_TEST_TARGET_TRIPLE.
@@ -234,7 +249,10 @@
   string(REPLACE "-" ";" TARGET_TRIPLE_LIST ${COMPILER_RT_DEFAULT_TARGET_TRIPLE})
   list(GET TARGET_TRIPLE_LIST 0 COMPILER_RT_DEFAULT_TARGET_ARCH)
   list(GET TARGET_TRIPLE_LIST 1 COMPILER_RT_DEFAULT_TARGET_OS)
-  list(GET TARGET_TRIPLE_LIST 2 COMPILER_RT_DEFAULT_TARGET_ABI)
+  list(LENGTH TARGET_TRIPLE_LIST TARGET_TRIPLE_LIST_LENGTH)
+  if(TARGET_TRIPLE_LIST_LENGTH GREATER 2)
+    list(GET TARGET_TRIPLE_LIST 2 COMPILER_RT_DEFAULT_TARGET_ABI)
+  endif()
   # Determine if test target triple is specified explicitly, and doesn't match the
   # default.
   if(NOT COMPILER_RT_DEFAULT_TARGET_TRIPLE STREQUAL TARGET_TRIPLE)
Index: compiler-rt/trunk/cmake/base-config-ix.cmake
===================================================================
--- compiler-rt/trunk/cmake/base-config-ix.cmake
+++ compiler-rt/trunk/cmake/base-config-ix.cmake
@@ -84,6 +84,8 @@
   option(COMPILER_RT_ENABLE_IOS "Enable building for iOS" On)
   option(COMPILER_RT_ENABLE_WATCHOS "Enable building for watchOS - Experimental" Off)
   option(COMPILER_RT_ENABLE_TVOS "Enable building for tvOS - Experimental" Off)
+else()
+  option(COMPILER_RT_DEFAULT_TARGET_ONLY "Build builtins only for the default target" Off)
 endif()
 
 if(WIN32 AND NOT MINGW AND NOT CYGWIN)
@@ -127,7 +129,9 @@
     detect_target_arch()
     set(COMPILER_RT_OS_SUFFIX "-android")
   elseif(NOT APPLE) # Supported archs for Apple platforms are generated later
-    if("${COMPILER_RT_DEFAULT_TARGET_ARCH}" MATCHES "i[2-6]86|x86|amd64")
+    if(COMPILER_RT_DEFAULT_TARGET_ONLY)
+      add_default_target_arch(${COMPILER_RT_DEFAULT_TARGET_ARCH})
+    elseif("${COMPILER_RT_DEFAULT_TARGET_ARCH}" MATCHES "i[2-6]86|x86|amd64")
       if(NOT MSVC)
         test_target_arch(x86_64 "" "-m64")
         # FIXME: We build runtimes for both i686 and i386, as "clang -m32" may
Index: compiler-rt/trunk/cmake/config-ix.cmake
===================================================================
--- compiler-rt/trunk/cmake/config-ix.cmake
+++ compiler-rt/trunk/cmake/config-ix.cmake
@@ -96,13 +96,6 @@
 set(SIMPLE_SOURCE ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/simple.cc)
 file(WRITE ${SIMPLE_SOURCE} "#include <stdlib.h>\n#include <stdio.h>\nint main() { printf(\"hello, world\"); }\n")
 
-# Add $arch as supported with no additional flags.
-macro(add_default_target_arch arch)
-  set(TARGET_${arch}_CFLAGS "")
-  set(CAN_TARGET_${arch} 1)
-  list(APPEND COMPILER_RT_SUPPORTED_ARCH ${arch})
-endmacro()
-
 # Detect whether the current target platform is 32-bit or 64-bit, and setup
 # the correct commandline flags needed to attempt to target 32-bit and 64-bit.
 if (NOT CMAKE_SIZEOF_VOID_P EQUAL 4 AND