As per discussion with Doug Gregor on the IRC channel, introduce a new compiler switch: -fms-compatility. 

Microsoft specific tweaking will now fall into 2 categories:

    - fms-extension: Microsoft specific extensions that should never change the meaning of an otherwise well formed code. Currently map to LangOptions::Microsoft. (To be clearer, I am planning to change the name to LangOptions::MicrosoftExt).

    - fms-compatibility: Really a MSVC emulation mode. Map to LangOptions::MicrosoftMode. Can change the meaning of an otherwise standard conformant program.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@139978 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Frontend/CompilerInvocation.cpp b/lib/Frontend/CompilerInvocation.cpp
index 582fcef..5f4310a 100644
--- a/lib/Frontend/CompilerInvocation.cpp
+++ b/lib/Frontend/CompilerInvocation.cpp
@@ -1655,6 +1655,7 @@
                                    Opts.DollarIdents);
   Opts.PascalStrings = Args.hasArg(OPT_fpascal_strings);
   Opts.Microsoft = Args.hasArg(OPT_fms_extensions);
+  Opts.MicrosoftMode = Args.hasArg(OPT_fms_compatibility);
   Opts.MSCVersion = Args.getLastArgIntValue(OPT_fmsc_version, 0, Diags);
   Opts.Borland = Args.hasArg(OPT_fborland_extensions);
   Opts.WritableStrings = Args.hasArg(OPT_fwritable_strings);