Rename the -import-tighter-objc-types option and add it to the frontend.

Swift SVN r19535

lib/Frontend/CompilerInvocation.cpp

@@ -611,6 +611,9 @@ static bool ParseClangImporterArgs(ClangImporterOptions &Opts, ArgList &Args,
   Opts.InferImplicitProperties |=
     Args.hasArg(OPT_enable_objc_implicit_properties);
 
+  Opts.ImportWithTighterObjCPointerTypes |=
+    Args.hasArg(OPT_import_tighter_objc_types);
+
   return false;
 }