The prefix 'Ms-' should be 'MS-'

Clang is otherwise consistent that Microsoft be abbreviated as MS, not
Ms.

llvm-svn: 227842
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index ab5c8f8..b5685d8 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -709,9 +709,9 @@
   if (Format == "clang")
     Opts.setFormat(DiagnosticOptions::Clang);
   else if (Format == "msvc")
-    Opts.setFormat(DiagnosticOptions::Msvc);
+    Opts.setFormat(DiagnosticOptions::MSVC);
   else if (Format == "msvc-fallback") {
-    Opts.setFormat(DiagnosticOptions::Msvc);
+    Opts.setFormat(DiagnosticOptions::MSVC);
     Opts.CLFallbackMode = true;
   } else if (Format == "vi")
     Opts.setFormat(DiagnosticOptions::Vi);