[C++2b] [Modules] Handle HaveModules with C++2b

Closing #56803. The root
cause for this bug is that we lack a good method to detect the language
mdoe when parsing the command line. There is a FIXME too. Dut to we lack
a good solution now, keep the workaround.

(cherry picked from commit 834a878)

Author: ChuanqiXu9

clang/lib/Driver/ToolChains/Clang.cpp

@@ -6588,7 +6588,7 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
   // support by default, or just assume that all languages do.
   bool HaveModules =
       Std && (Std->containsValue("c++2a") || Std->containsValue("c++20") ||
-              Std->containsValue("c++latest"));
+              Std->containsValue("c++2b") || Std->containsValue("c++latest"));
   RenderModulesOptions(C, D, Args, Input, Output, CmdArgs, HaveModules);
 
   if (Args.hasFlag(options::OPT_fpch_validate_input_files_content,

clang/test/Driver/modules-fprebuilt-mdoule-path.cpp

@@ -0,0 +1,7 @@
+// RUN: %clang -std=c++2a -fprebuilt-module-path=. -### -c %s 2>&1 | FileCheck %s
+// RUN: %clang -std=c++20 -fprebuilt-module-path=. -### -c %s 2>&1 | FileCheck %s
+// RUN: %clang -std=c++2b -fprebuilt-module-path=. -### -c %s 2>&1 | FileCheck %s
+// RUN: %clang -std=c++latest -fprebuilt-module-path=. -### -c %s 2>&1 | FileCheck %s
+//
+// CHECK-NOT: warning: argument unused during compilation
+// CHECK: -fprebuilt-module-path=.