[PATCH] Driver: enhance MSC version compatibility

[Reid Kleckner]

lgtm with a simplification

================
Comment at: lib/Frontend/CompilerInvocation.cpp:1197
@@ +1196,3 @@
+                            DiagnosticsEngine &Diags) {
+  decltype(Opts.MSCVersion) Version = 0;
+
----------------
I don't think this decltype stuff is necessary.  LLVM assumes unsigned is 32-bit in lots of other places.  I'd rather have this return 'unsigned', not take LangOpts, and have the caller assign the result to Opts.MSCVersion.

http://reviews.llvm.org/D4233