Convert MC command line flag for fatal assembler warnings into a proper
flag.

llvm-svn: 216472
diff --git a/clang/lib/Driver/Tools.cpp b/clang/lib/Driver/Tools.cpp
index 0813089..db1a48e 100644
--- a/clang/lib/Driver/Tools.cpp
+++ b/clang/lib/Driver/Tools.cpp
@@ -2043,8 +2043,7 @@
         } else if (Value == "-L") {
           CmdArgs.push_back("-msave-temp-labels");
         } else if (Value == "--fatal-warnings") {
-          CmdArgs.push_back("-mllvm");
-          CmdArgs.push_back("-fatal-assembler-warnings");
+          CmdArgs.push_back("-massembler-fatal-warnings");
         } else if (Value == "--noexecstack") {
           CmdArgs.push_back("-mnoexecstack");
         } else if (Value == "-compress-debug-sections" ||