More clang support for darwin tls.  Add a __has_feature macro and
target specific preprocessor define as well.

llvm-svn: 106715
diff --git a/clang/lib/Basic/Targets.cpp b/clang/lib/Basic/Targets.cpp
index 3717b12..12758f8 100644
--- a/clang/lib/Basic/Targets.cpp
+++ b/clang/lib/Basic/Targets.cpp
@@ -150,7 +150,7 @@
 public:
   DarwinTargetInfo(const std::string& triple) :
     OSTargetInfo<Target>(triple) {
-      this->TLSSupported = false;
+      this->TLSSupported = llvm::Triple(triple).getDarwinMajorNumber() > 6;
     }
 
   virtual std::string isValidSectionSpecifier(llvm::StringRef SR) const {