Driver: implement addClangWarningOptions

This function allows certain platforms to enable or disable diagnostics
by default.

llvm-svn: 205095
diff --git a/clang/lib/Driver/Tools.cpp b/clang/lib/Driver/Tools.cpp
index 9a31eb9..0c39758 100644
--- a/clang/lib/Driver/Tools.cpp
+++ b/clang/lib/Driver/Tools.cpp
@@ -2116,6 +2116,11 @@
   std::string TripleStr = getToolChain().ComputeEffectiveClangTriple(Args);
   CmdArgs.push_back(Args.MakeArgString(TripleStr));
 
+  // Push all default warning arguments that are specific to
+  // the given target.  These come before user provided warning options
+  // are provided.
+  getToolChain().addClangWarningOptions(CmdArgs);
+
   // Select the appropriate action.
   RewriteKind rewriteKind = RK_None;