[Support] sys::getProcessTriple should return a macOS triple using
the system's version of macOS

sys::getProcessTriple returns LLVM_HOST_TRIPLE, whose system version might not
be the actual version of the system on which the compiler running. This commit
ensures that, for macOS, sys::getProcessTriple returns a triple with the
system's macOS version.

rdar://33177551

Differential Revision: https://reviews.llvm.org/D34446

llvm-svn: 307372
diff --git a/llvm/lib/Support/Host.cpp b/llvm/lib/Support/Host.cpp
index 232efe6..31d43fe 100644
--- a/llvm/lib/Support/Host.cpp
+++ b/llvm/lib/Support/Host.cpp
@@ -1494,7 +1494,8 @@
 #endif
 
 std::string sys::getProcessTriple() {
-  Triple PT(Triple::normalize(LLVM_HOST_TRIPLE));
+  std::string TargetTripleString = updateTripleOSVersion(LLVM_HOST_TRIPLE);
+  Triple PT(Triple::normalize(TargetTripleString));
 
   if (sizeof(void *) == 8 && PT.isArch32Bit())
     PT = PT.get64BitArchVariant();