[Driver] Fix --hash-style choice for Android.

[danalbert]

Summary

Android supports GNU style hashes as of Marshmallow, so we should be
generating both styles for pre-M targets and GNU hashes for newer
targets.

lib/Driver/ToolChains/Linux.cpp

Linux::Linux(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
 
   if (IsMips && !SysRoot.empty())
     ExtraOpts.push_back("--sysroot=" + SysRoot);
 
   // Do not use 'gnu' hash style for Mips targets because .gnu.hash
   // and the MIPS ABI require .dynsym to be sorted in different ways.
   // .gnu.hash needs symbols to be grouped by hash code whereas the MIPS
   // ABI requires a mapping between the GOT and the symbol table.
-  // Android loader does not support .gnu.hash.
+  // Android loader does not support .gnu.hash until API 23.
   // Hexagon linker/loader does not support .gnu.hash
-  if (!IsMips && !IsAndroid && !IsHexagon) {
+  if (!IsMips && !IsHexagon) {
     if (Distro.IsRedhat() || Distro.IsOpenSUSE() || Distro.IsAlpineLinux() ||
-        (Distro.IsUbuntu() && Distro >= Distro::UbuntuMaverick))
+        (Distro.IsUbuntu() && Distro >= Distro::UbuntuMaverick) ||
+        (IsAndroid && !Triple.isAndroidVersionLT(23)))
       ExtraOpts.push_back("--hash-style=gnu");
 
-    if (Distro.IsDebian() || Distro.IsOpenSUSE() || Distro == Distro::UbuntuLucid ||
-        Distro == Distro::UbuntuJaunty || Distro == Distro::UbuntuKarmic)
+    if (Distro.IsDebian() || Distro.IsOpenSUSE() ||
+        Distro == Distro::UbuntuLucid || Distro == Distro::UbuntuJaunty ||
+        Distro == Distro::UbuntuKarmic ||
+        (IsAndroid && Triple.isAndroidVersionLT(23)))
       ExtraOpts.push_back("--hash-style=both");
   }
 
   if (Distro.IsRedhat() && Distro != Distro::RHEL5 && Distro != Distro::RHEL6)
     ExtraOpts.push_back("--no-add-needed");
 
 #ifdef ENABLE_LINKER_BUILD_ID
   ExtraOpts.push_back("--build-id");

test/Driver/linux-ld.c

 //
 // RUN: %clang %s -### -o %t.o 2>&1 --target=mips64el-redhat-linux \
 // RUN:   | FileCheck --check-prefix=CHECK-MIPS64EL-REDHAT %s
 // CHECK-MIPS64EL-REDHAT: "{{.*}}ld{{(.exe)?}}"
 // CHECK-MIPS64EL-REDHAT: "-m" "elf64ltsmip"
 // CHECK-MIPS64EL-REDHAT: "-dynamic-linker" "{{.*}}/lib{{(64)?}}/ld.so.1"
 // CHECK-MIPS64EL-REDHAT-NOT: "-dynamic-linker" "{{.*}}/lib{{(64)?}}/ld-musl-mipsel.so.1"
 // CHECK-MIPS64EL-REDHAT-NOT: "--hash-style={{gnu|both}}"
+
+// Check that we pass --hash-style=both for pre-M Android versions and
+// --hash-style=gnu for newer Android versions.
+// RUN: %clang %s -### -o %t.o 2>&1 \
+// RUN:     --target=armv7-linux-android21 \
+// RUN:   | FileCheck --check-prefix=CHECK-ANDROID-HASH-STYLE-L %s
+// CHECK-ANDROID-HASH-STYLE-L: "{{.*}}ld{{(.exe)?}}"
+// CHECK-ANDROID-HASH-STYLE-L: "--hash-style=both"
+//
+// RUN: %clang %s -### -o %t.o 2>&1 \
+// RUN:     --target=armv7-linux-android23 \
+// RUN:   | FileCheck --check-prefix=CHECK-ANDROID-HASH-STYLE-M %s
+// CHECK-ANDROID-HASH-STYLE-M: "{{.*}}ld{{(.exe)?}}"
+// CHECK-ANDROID-HASH-STYLE-M: "--hash-style=gnu"
 //
 // RUN: %clang %s -### -o %t.o 2>&1 \
 // RUN:     --target=sparc-unknown-linux-gnu \
 // RUN:   | FileCheck --check-prefix=CHECK-SPARCV8 %s
 // CHECK-SPARCV8: "{{.*}}ld{{(.exe)?}}"
 // CHECK-SPARCV8: "-m" "elf32_sparc"
 // CHECK-SPARCV8: "-dynamic-linker" "{{(/usr/sparc-unknown-linux-gnu)?}}/lib/ld-linux.so.2"
 //