[clang-cl]: Don't warn on /bigobj flag

[thakis]

Summary

LLVM r217812 made it so that clang-cl implicitly creates bigobj files when needed, independent of this flag. It looks like cl has this flag to produce obj flags compatible with MSVS 2003's linker by default, something we don't care about. Since clang-cl always has /bigobj behavior, don't warn that the flag is unused, just ignore it silently.

[hans]

LGTM

Please also add this to the tests for ignored options in test/Driver/cl-options.c:221

[thakis]

r248034, thanks! (with test)

include/clang/Driver/CLCompatOptions.td

def _SLASH_volatile_ms  : Option<["/", "-"], "volatile:ms", KIND_FLAG>,
   Group<_SLASH_volatile_Group>, Flags<[CLOption, DriverOption]>,
   HelpText<"Volatile loads and stores have acquire and release semantics">;
 def _SLASH_Zl : CLFlag<"Zl">,
   HelpText<"Don't mention any default libraries in the object file">;
 
 // Ignored:
 
 def _SLASH_analyze_ : CLIgnoredFlag<"analyze-">;
+def _SLASH_bigobj : CLIgnoredFlag<"bigobj">;
 def _SLASH_cgthreads : CLIgnoredJoined<"cgthreads">;
 def _SLASH_d2Zi_PLUS : CLIgnoredFlag<"d2Zi+">;
 def _SLASH_errorReport : CLIgnoredJoined<"errorReport">;
 def _SLASH_Fd : CLIgnoredJoined<"Fd">;
 def _SLASH_FS : CLIgnoredFlag<"FS">, HelpText<"Force synchronous PDB writes">;
 def _SLASH_Gd : CLIgnoredFlag<"Gd">;
 def _SLASH_GF : CLIgnoredFlag<"GF">;
 def _SLASH_GS_ : CLIgnoredFlag<"GS-">;

 def _SLASH_Zm : CLIgnoredJoined<"Zm">;
 def _SLASH_Zo : CLIgnoredFlag<"Zo">;
 def _SLASH_Zo_ : CLIgnoredFlag<"Zo-">;
 
 
 // Unsupported:
 
 def _SLASH_AI : CLJoined<"AI">;
-def _SLASH_bigobj : CLFlag<"bigobj">;
 def _SLASH_clr : CLJoined<"clr">;
 def _SLASH_doc : CLJoined<"doc">;
 def _SLASH_FA_joined : CLJoined<"FA">;
 def _SLASH_favor : CLJoined<"favor">;
 def _SLASH_FC : CLFlag<"FC">;
 def _SLASH_F : CLFlag<"F">;
 def _SLASH_Fm : CLJoined<"Fm">;
 def _SLASH_Fp : CLJoined<"Fp">;