[OpenCL] Allow for variadic macros in C++ for OpenCL

[olestrohm]

Summary

C++ for OpenCL intends to support variadic macros, a decision motivated by OpenCL 3.0. This patch simply skips the warning when compiling in C++ for OpenCL mode.

[Anastasia]

Can you extend test test/Preprocessor/macro_variadic.cl to cover C++ for OpenCL mode, otherwise LGTM!

[olestrohm]

I have amended the relevant test to validate this behaviour in C++ for OpenCL.

[Anastasia]

LGTM! Thanks

clang/lib/Lex/PPDirectives.cpp

case tok::r_paren:
       return true;
     case tok::ellipsis:  // #define X(... -> C99 varargs
       if (!LangOpts.C99)
         Diag(Tok, LangOpts.CPlusPlus11 ?
              diag::warn_cxx98_compat_variadic_macro :
              diag::ext_variadic_macro);
 
       // OpenCL v1.2 s6.9.e: variadic macros are not supported.
-      if (LangOpts.OpenCL) {
+      if (LangOpts.OpenCL && !LangOpts.OpenCLCPlusPlus) {
         Diag(Tok, diag::ext_pp_opencl_variadic_macros);
       }
 
       // Lex the token after the identifier.
       LexUnexpandedToken(Tok);
       if (Tok.isNot(tok::r_paren)) {
         Diag(Tok, diag::err_pp_missing_rparen_in_macro_def);
         return true;