Restore GNU , ## __VA_ARGS__ behavior in MSVC mode

As noted in D91913, MSVC implements the GNU behavior for
, ## __VA_ARGS__ as well. Do the same when `-fms-compatibility` is used.

Reviewed By: rsmith

Differential Revision: https://reviews.llvm.org/D95392

Author: hvdijk

clang/lib/Lex/TokenLexer.cpp

@@ -152,7 +152,8 @@ bool TokenLexer::MaybeRemoveCommaBeforeVaArgs(
   // named arguments, where it remains.  With GNU extensions, it is removed
   // regardless of named arguments.
   // Microsoft also appears to support this extension, unofficially.
-  if (!PP.getLangOpts().GNUMode && Macro->getNumParams() < 2)
+  if (!PP.getLangOpts().GNUMode && !PP.getLangOpts().MSVCCompat &&
+      Macro->getNumParams() < 2)
     return false;
 
   // Is a comma available to be removed?

clang/test/Preprocessor/macro_fn_comma_swallow2.c

@@ -9,6 +9,8 @@
 // RUN: %clang_cc1 -E -x c++ -std=c++11 %s | FileCheck -check-prefix=C99 -strict-whitespace %s
 // RUN: %clang_cc1 -E -std=gnu99 %s | FileCheck -check-prefix=GCC -strict-whitespace %s
 // RUN: %clang_cc1 -E -fms-compatibility %s | FileCheck -check-prefix=MS -strict-whitespace %s
+// RUN: %clang_cc1 -E -x c++ -fms-compatibility %s | FileCheck -check-prefix=MS -strict-whitespace %s
+// RUN: %clang_cc1 -E -x c++ -std=c++11 -fms-compatibility %s | FileCheck -check-prefix=MS -strict-whitespace %s
 // RUN: %clang_cc1 -E -DNAMED %s | FileCheck -check-prefix=GCC -strict-whitespace %s
 // RUN: %clang_cc1 -E -std=c99 -DNAMED %s | FileCheck -check-prefix=C99 -strict-whitespace %s