ADT/Triple: Add isOSDarwin() and isOSWindows() helper functions.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@129815 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Support/Triple.cpp b/lib/Support/Triple.cpp
index 51f6c07..8281b48 100644
--- a/lib/Support/Triple.cpp
+++ b/lib/Support/Triple.cpp
@@ -213,8 +213,7 @@
 
 // Returns architecture name that is understood by the target assembler.
 const char *Triple::getArchNameForAssembler() {
-  if (getOS() != Triple::Darwin && getOS() != Triple::OSX &&
-      getOS() != Triple::IOS && getVendor() != Triple::Apple)
+  if (!isOSDarwin() && getVendor() != Triple::Apple)
     return NULL;
 
   StringRef Str = getArchName();