[driver][xray] fix the macOS support checker by supporting -macos triple in addition to -darwin

[arphaman]

Summary

The previous check incorrectly checked for macOS support by allowing -darwin triples only, and -macos triple was not supported.

[dberris]

LGTM -- apologies for the delay, I hope this isn't too late.

cfe/trunk/lib/Driver/XRayArgs.cpp

if (Triple.getOS() == llvm::Triple::Linux) {
         break;
       default:
         D.Diag(diag::err_drv_clang_unsupported)
             << (std::string(XRayInstrumentOption) + " on " + Triple.str());
       }
     } else if (Triple.isOSFreeBSD() ||
                Triple.isOSOpenBSD() ||
                Triple.isOSNetBSD() ||
-               Triple.getOS() == llvm::Triple::Darwin) {
+               Triple.isMacOSX()) {
       if (Triple.getArch() != llvm::Triple::x86_64) {
         D.Diag(diag::err_drv_clang_unsupported)
             << (std::string(XRayInstrumentOption) + " on " + Triple.str());
       }
     } else if (Triple.getOS() == llvm::Triple::Fuchsia) {
       switch (Triple.getArch()) {
       case llvm::Triple::x86_64:
       case llvm::Triple::aarch64:

cfe/trunk/test/Driver/XRay/xray-instrument-macos.c

+// RUN: %clang -o /dev/null -v -fxray-instrument -target x86_64-apple-macos10.11 -c %s
+// RUN: %clang -o /dev/null -v -fxray-instrument -target x86_64-apple-darwin15 -c %s
+// REQUIRES-ANY: x86_64, x86_64h
+typedef int a;