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/ToolChain.cpp b/lib/Driver/ToolChain.cpp
index 074f1a3..d09ab16 100644
--- a/lib/Driver/ToolChain.cpp
+++ b/lib/Driver/ToolChain.cpp
@@ -185,8 +185,7 @@
     // FIXME: Thumb should just be another -target-feaure, not in the triple.
     StringRef Suffix =
       getLLVMArchSuffixForARM(getARMTargetCPU(Args, Triple));
-    bool ThumbDefault =
-      (Suffix == "v7" && getTriple().getOS() == llvm::Triple::Darwin);
+    bool ThumbDefault = (Suffix == "v7" && getTriple().isOSDarwin());
     std::string ArchName = "arm";
 
     // Assembly files should start in ARM mode.