Fix crash with x86_64-pc-win32-macho target. <rdar://problem/17235840>

The changes in r204978 broke win32-macho targets. There were checks added for
MSVC and Itanium environments as special cases, and win32-macho needs to be
treated the same way.

llvm-svn: 210584

clang/lib/Frontend/InitHeaderSearch.cpp

@@ -472,7 +472,8 @@ void InitHeaderSearch::AddDefaultIncludePaths(const LangOptions &Lang,
 
   case llvm::Triple::Win32:
     if (triple.getEnvironment() == llvm::Triple::MSVC ||
-        triple.getEnvironment() == llvm::Triple::Itanium)
+        triple.getEnvironment() == llvm::Triple::Itanium ||
+        triple.getObjectFormat() == llvm::Triple::MachO)
       return;
     break;
   }

clang/test/Misc/win32-macho.c

@@ -0,0 +1,2 @@
+// Check that basic use of win32-macho targets works.
+// RUN: %clang -c -target x86_64-pc-win32-macho %s