[Modules] Allow local submodule visibility without c++

[bruno]

Summary

Removing this restriction will make it handy to explore local submodule visibility without c++ being turned on. We're currently testing it out with C/ObjC.

[rsmith]

Can you also add a basic test that this works in C? Thanks!

cfe/trunk/lib/Frontend/CompilerInvocation.cpp

#include "clang/Frontend/LangStandards.def"
   // CUDA extension. However, it is required for supporting
   // __clang_cuda_builtin_vars.h, which uses __declspec(property). Once that has
   // been rewritten in terms of something more generic, remove the Opts.CUDA
   // term here.
   Opts.DeclSpecKeyword =
       Args.hasFlag(OPT_fdeclspec, OPT_fno_declspec,
                    (Opts.MicrosoftExt || Opts.Borland || Opts.CUDA));
 
-  // For now, we only support local submodule visibility in C++ (because we
-  // heavily depend on the ODR for merging redefinitions).
-  if (Opts.ModulesLocalVisibility && !Opts.CPlusPlus)
-    Diags.Report(diag::err_drv_argument_not_allowed_with)
-        << "-fmodules-local-submodule-visibility" << "C";
-
   if (Arg *A = Args.getLastArg(OPT_faddress_space_map_mangling_EQ)) {
     switch (llvm::StringSwitch<unsigned>(A->getValue())
       .Case("target", LangOptions::ASMM_Target)
       .Case("no", LangOptions::ASMM_Off)
       .Case("yes", LangOptions::ASMM_On)
       .Default(255)) {
     default:
       Diags.Report(diag::err_drv_invalid_value)

cfe/trunk/test/Modules/localsubmodulevis.m

+// RUN: rm -rf %t
+// RUN: %clang_cc1 -fmodules -fmodules-local-submodule-visibility -fimplicit-module-maps -fmodules-cache-path=%t.a -I %S/Inputs/preprocess -verify %s
+// RUN: %clang_cc1 -fmodules -fmodules-local-submodule-visibility -fimplicit-module-maps -fmodules-cache-path=%t.b -I %S/Inputs/preprocess -x c -verify -x c %s
+
+// expected-no-diagnostics
+
+#include "file.h"
+