clang-cl: Accept (and ignore) /Zc:__cplusplus.

[thakis]

Summary

See https://blogs.msdn.microsoft.com/vcblog/2018/04/09/msvc-now-correctly-reports-__cplusplus/

clang-cl already sets __cplusplus to the correct value, so we can just ignore this flag.

Also add test coverage for a few more accepted-but-ignored flags.

[hans]

lgtm, thanks!

[thakis]

r330427, thanks!

include/clang/Driver/CLCompatOptions.td

 def _SLASH_openmp_ : CLIgnoredFlag<"openmp-">;
 def _SLASH_permissive_ : CLIgnoredFlag<"permissive-">;
 def _SLASH_RTC : CLIgnoredJoined<"RTC">;
 def _SLASH_sdl : CLIgnoredFlag<"sdl">;
 def _SLASH_sdl_ : CLIgnoredFlag<"sdl-">;
 def _SLASH_utf8 : CLIgnoredFlag<"utf-8">,
   HelpText<"Set source and runtime encoding to UTF-8 (default)">;
 def _SLASH_w : CLIgnoredJoined<"w">;
+def _SLASH_Zc___cplusplus : CLIgnoredFlag<"Zc:__cplusplus">;
 def _SLASH_Zc_auto : CLIgnoredFlag<"Zc:auto">;
 def _SLASH_Zc_forScope : CLIgnoredFlag<"Zc:forScope">;
 def _SLASH_Zc_inline : CLIgnoredFlag<"Zc:inline">;
 def _SLASH_Zc_rvalueCast : CLIgnoredFlag<"Zc:rvalueCast">;
-def _SLASH_Zc_wchar_t : CLIgnoredFlag<"Zc:wchar_t">;
 def _SLASH_Zc_ternary : CLIgnoredFlag<"Zc:ternary">;
+def _SLASH_Zc_wchar_t : CLIgnoredFlag<"Zc:wchar_t">;
 def _SLASH_Zm : CLIgnoredJoined<"Zm">;
 def _SLASH_Zo : CLIgnoredFlag<"Zo">;
 def _SLASH_Zo_ : CLIgnoredFlag<"Zo-">;
 
 
 // Unsupported:
 
 def _SLASH_AI : CLJoined<"AI">;

test/Driver/cl-options.c

 // RUN:    /FC \
 // RUN:    /Fdfoo \
 // RUN:    /FS \
 // RUN:    /Gd \
 // RUN:    /GF \
 // RUN:    /GS- \
 // RUN:    /kernel- \
 // RUN:    /nologo \
+// RUN:    /Og \
 // RUN:    /openmp- \
 // RUN:    /permissive- \
 // RUN:    /RTC1 \
 // RUN:    /sdl \
 // RUN:    /sdl- \
 // RUN:    /source-charset:utf-8 \
 // RUN:    /utf-8 \
 // RUN:    /vmg \
 // RUN:    /volatile:iso \
 // RUN:    /w12345 \
 // RUN:    /wd1234 \
+// RUN:    /Zc:__cplusplus \
+// RUN:    /Zc:auto \
+// RUN:    /Zc:forScope \
+// RUN:    /Zc:inline \
+// RUN:    /Zc:rvalueCast \
+// RUN:    /Zc:ternary \
+// RUN:    /Zc:wchar_t \
+// RUN:    /Zm \
 // RUN:    /Zo \
 // RUN:    /Zo- \
 // RUN:    -### -- %s 2>&1 | FileCheck -check-prefix=IGNORED %s
 // IGNORED-NOT: argument unused during compilation
 // IGNORED-NOT: no such file or directory
 // Don't confuse /openmp- with the /o flag:
 // IGNORED-NOT: "-o" "penmp-.obj"