[clang] [clang][modules-driver] Add scanner to detect C++20 module presence (PR #145220)

[Michael Spencer via cfe-commits]

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@@ -577,6 +577,19 @@ def err_drv_reduced_module_output_overrided : Warning<
   "please consider use '-fmodule-output=' to specify the output file for reduced BMI explicitly">,
   InGroup<DiagGroup<"reduced-bmi-output-overrided">>;
 
+def remark_fmodules_driver_enabled : Remark<
+  "support for explicit module builds enabled (experimental)">,
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Bigcheese wrote:

I don't think this specific remark is needed, it's just saying the flag is passed, which is simple enough to not need a remark for.

https://github.com/llvm/llvm-project/pull/145220