MachO: use "arm64" as the triple name in modules.

Current versions of ld64 can't cope with "aarch64" being stored. I'm fixing
that, but in the transitionary period we'll need to still emit "arm64".

rdar://problem/17783765

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@213852 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Driver/ToolChain.cpp

@@ -221,6 +221,17 @@ std::string ToolChain::ComputeLLVMTriple(const ArgList &Args,
     }
     return Triple.getTriple();
   }
+  case llvm::Triple::aarch64: {
+    llvm::Triple Triple = getTriple();
+    if (!Triple.isOSBinFormatMachO())
+      return getTripleString();
+
+    // FIXME: older versions of ld64 expect the "arm64" component in the actual
+    // triple string and query it to determine whether an LTO file can be
+    // handled. Remove this when we don't care any more.
+    Triple.setArchName("arm64");
+    return Triple.getTriple();
+  }
   case llvm::Triple::arm:
   case llvm::Triple::armeb:
   case llvm::Triple::thumb:

test/Driver/aarch64-cpus.c

@@ -11,7 +11,7 @@
 // ARM64-GENERIC: "-cc1"{{.*}} "-triple" "arm64{{.*}}" "-target-cpu" "generic"
 
 // RUN: %clang -target arm64-apple-darwin -arch arm64 -### -c %s 2>&1 | FileCheck -check-prefix=ARM64-DARWIN %s
-// ARM64-DARWIN: "-cc1"{{.*}} "-triple" "aarch64{{.*}}" "-target-cpu" "cyclone"
+// ARM64-DARWIN: "-cc1"{{.*}} "-triple" "arm64{{.*}}" "-target-cpu" "cyclone"
 
 // RUN: %clang -target aarch64 -mcpu=cortex-a53 -### -c %s 2>&1 | FileCheck -check-prefix=CA53 %s
 // RUN: %clang -target aarch64 -mlittle-endian -mcpu=cortex-a53 -### -c %s 2>&1 | FileCheck -check-prefix=CA53 %s