now that we have a centralized place to do so, add some using declarations for
some common llvm types: stringref and smallvector.  This cleans up the codebase
quite a bit.

llvm-svn: 135576
diff --git a/clang/lib/Driver/ToolChains.h b/clang/lib/Driver/ToolChains.h
index d68016b..24545ec 100644
--- a/clang/lib/Driver/ToolChains.h
+++ b/clang/lib/Driver/ToolChains.h
@@ -139,7 +139,7 @@
   /// getDarwinArchName - Get the "Darwin" arch name for a particular compiler
   /// invocation. For example, Darwin treats different ARM variations as
   /// distinct architectures.
-  llvm::StringRef getDarwinArchName(const ArgList &Args) const;
+  StringRef getDarwinArchName(const ArgList &Args) const;
 
   static bool isVersionLT(unsigned (&A)[3], unsigned (&B)[3]) {
     for (unsigned i=0; i < 3; ++i) {