[clang/Driver] Also consider `gnu++` standard when checking for modules support

[akyrtzi]

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clang/lib/Driver/ToolChains/Clang.cpp

static bool RenderModulesOptions(Compilation &C, const Driver &D,
                                  const ArgList &Args, const InputInfo &Input,
                                  const InputInfo &Output, const Arg *Std,
                                  ArgStringList &CmdArgs) {
   bool IsCXX = types::isCXX(Input.getType());
   // FIXME: Find a better way to determine whether the input has standard c++
   // modules support by default.
   bool HaveStdCXXModules =
       IsCXX && Std &&
-      (Std->containsValue("c++2a") || Std->containsValue("c++20") ||
-       Std->containsValue("c++2b") || Std->containsValue("c++23") ||
-       Std->containsValue("c++latest"));
+      (Std->containsValue("c++2a") || Std->containsValue("gnu++2a") ||
+       Std->containsValue("c++20") || Std->containsValue("gnu++20") ||
+       Std->containsValue("c++2b") || Std->containsValue("gnu++2b") ||
+       Std->containsValue("c++23") || Std->containsValue("gnu++23") ||
+       Std->containsValue("c++latest") || Std->containsValue("gnu++latest"));
   bool HaveModules = HaveStdCXXModules;
 
   // -fmodules enables the use of precompiled modules (off by default).
   // Users can pass -fno-cxx-modules to turn off modules support for
   // C++/Objective-C++ programs.
   bool HaveClangModules = false;
   if (Args.hasFlag(options::OPT_fmodules, options::OPT_fno_modules, false)) {
     bool AllowedInCXX = Args.hasFlag(options::OPT_fcxx_modules,

clang/test/Driver/modules.cpp

 // RUN: rm -rf %t
 // RUN: mkdir %t
 
 // Check compiling a module interface to a .pcm file.
 //
 // RUN: %clang -std=c++2a -x c++-module --precompile %s -o %t/module.pcm -v 2>&1 | FileCheck %s --check-prefix=CHECK-PRECOMPILE
+// RUN: %clang -std=gnu++2a -x c++-module --precompile %s -o %t/module-gnu.pcm -v 2>&1 | FileCheck %s --check-prefix=CHECK-PRECOMPILE
 //
 // CHECK-PRECOMPILE: -cc1 {{.*}} -emit-module-interface
 // CHECK-PRECOMPILE-SAME: -o {{.*}}.pcm
 // CHECK-PRECOMPILE-SAME: -x c++
 // CHECK-PRECOMPILE-SAME: modules.cpp
 
 // Check compiling a .pcm file to a .o file.
 //
 // RUN: %clang -std=c++2a %t/module.pcm -S -o %t/module.pcm.o -v 2>&1 | FileCheck %s --check-prefix=CHECK-COMPILE
 //
 // CHECK-COMPILE: -cc1 {{.*}} {{-emit-obj|-S}}
 // CHECK-COMPILE-SAME: -o {{.*}}module{{2*}}.pcm.o
 // CHECK-COMPILE-SAME: -x pcm
 // CHECK-COMPILE-SAME: {{.*}}.pcm
 
 // Check use of a .pcm file in another compilation.
 //
 // RUN: %clang -std=c++2a -fmodule-file=%t/module.pcm -Dexport= %s -S -o %t/module.o -v 2>&1 | FileCheck %s --check-prefix=CHECK-USE
 // RUN: %clang -std=c++20 -fmodule-file=%t/module.pcm -Dexport= %s -S -o %t/module.o -v 2>&1 | FileCheck %s --check-prefix=CHECK-USE
+// RUN: %clang -std=gnu++20 -fmodule-file=%t/module-gnu.pcm -Dexport= %s -S -o %t/module.o -v 2>&1 | FileCheck %s --check-prefix=CHECK-USE
 //
 // CHECK-USE: -cc1 {{.*}} {{-emit-obj|-S}}
 // CHECK-USE-SAME: -fmodule-file={{.*}}.pcm
 // CHECK-USE-SAME: -o {{.*}}.{{o|s}}{{"?}} {{.*}}-x c++
 // CHECK-USE-SAME: modules.cpp
 
 // Check combining precompile and compile steps works.
 //
 // RUN: %clang -std=c++2a -x c++-module %s -S -o %t/module2.pcm.o -v 2>&1 | FileCheck %s --check-prefix=CHECK-PRECOMPILE --check-prefix=CHECK-COMPILE
 
 // Check that .cppm is treated as a module implicitly.
 //
 // RUN: cp %s %t/module.cppm
 // RUN: %clang -std=c++2a --precompile %t/module.cppm -o %t/module.pcm -v 2>&1 | FileCheck %s --check-prefix=CHECK-PRECOMPILE
 
 export module foo;