Don't complain about -fobjc-link-runtime being unused with -fobjc-arc.

If you build with -fobjc-arc, then -fobjc-link-runtime is implied but we
don't need to warn about it being unused in that case.  rdar://12039965

llvm-svn: 161444
diff --git a/clang/lib/Driver/Tools.cpp b/clang/lib/Driver/Tools.cpp
index a096382..fcd61b7 100644
--- a/clang/lib/Driver/Tools.cpp
+++ b/clang/lib/Driver/Tools.cpp
@@ -174,8 +174,10 @@
 
 /// \brief Determine whether we are linking the ObjC runtime.
 static bool isObjCRuntimeLinked(const ArgList &Args) {
-  if (isObjCAutoRefCount(Args))
+  if (isObjCAutoRefCount(Args)) {
+    Args.ClaimAllArgs(options::OPT_fobjc_link_runtime);
     return true;
+  }
   return Args.hasArg(options::OPT_fobjc_link_runtime);
 }