Use Triple.isOSDarwin() instead of comparing against Triple::Darwin.

There are now separate Triple::MacOSX and Triple::IOS values for the OS
so comparing against Triple::Darwin will fail to match those.  Note that
I changed the expected output for the Driver/rewrite-objc.m test, which had
previously not been passing Darwin-specific options with the macosx triple.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@141944 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Driver/ToolChains.cpp b/lib/Driver/ToolChains.cpp
index 1edb56a..0fa25fb 100644
--- a/lib/Driver/ToolChains.cpp
+++ b/lib/Driver/ToolChains.cpp
@@ -200,7 +200,7 @@
     // Fallback to llvm-gcc for i386 kext compiles, we don't support that ABI.
     if (Inputs.size() == 1 &&
         types::isCXX(Inputs[0]->getType()) &&
-        getTriple().getOS() == llvm::Triple::Darwin &&
+        getTriple().isOSDarwin() &&
         getTriple().getArch() == llvm::Triple::x86 &&
         (C.getArgs().getLastArg(options::OPT_fapple_kext) ||
          C.getArgs().getLastArg(options::OPT_mkernel)))