[clang][cli] Stop creating '-Wno-stdlibcxx-not-found' in cc1

[jansvoboda11]

Summary

This patch stops creating the '-Wno-stdlibcxx-not-found' argument in CompilerInvocation::CreateFromArgs.

The code was added in 2e7ab55e657f (a follow-up to D48297). However, D61963 removes relevant tests and starts explicitly passing '-Wno-stdlibcxx-not-found' to the driver. I think it's fair to assume this is a dead code.

[dexonsmith]

Agreed; LGTM.

[dexonsmith]

In D97042#2576372, @dexonsmith wrote:

Agreed; LGTM.

To be more explicit, here's how I confirmed this is dead code: warn_drv_libstdcxx_not_found is the only warning in DiagGroup<"stdlibcxx-not-found"> and it's only used by clang/lib/Driver/ToolChains/Darwin.cpp. It cannot have an effect on -cc1.

clang/lib/Frontend/CompilerInvocation.cpp

parseSanitizerKinds("-fsanitize=", Args.getAllArgValues(OPT_fsanitize_EQ),
                         Diags, LangOpts.Sanitize);
   } else {
     // Other LangOpts are only initialized when the input is not AST or LLVM IR.
     // FIXME: Should we really be calling this for an Language::Asm input?
     Success &= ParseLangArgs(Res, LangOpts, Args, DashX, T,
                              Res.getPreprocessorOpts().Includes, Diags);
     if (Res.getFrontendOpts().ProgramAction == frontend::RewriteObjC)
       LangOpts.ObjCExceptions = 1;
-    if (T.isOSDarwin() && DashX.isPreprocessed()) {
-      // Supress the darwin-specific 'stdlibcxx-not-found' diagnostic for
-      // preprocessed input as we don't expect it to be used with -std=libc++
-      // anyway.
-      Res.getDiagnosticOpts().Warnings.push_back("no-stdlibcxx-not-found");
-    }
   }
 
   if (LangOpts.CUDA) {
     // During CUDA device-side compilation, the aux triple is the
     // triple used for host compilation.
     if (LangOpts.CUDAIsDevice)
       Res.getTargetOpts().HostTriple = Res.getFrontendOpts().AuxTriple;
   }