when using clang-cl, --precompile seems to force the pcm file to be generated in the directory when clang is invoked instead of respecting -fmodule-output
// test.mpp
export module Test;
> F:\llvm\bin\clang-cl -std:c++20 -x c++-module -fmodule-output=a\test.pcm test.mpp -c
> F:\llvm\bin\clang-cl -std:c++20 -x c++-module -fmodule-output=a\test.pcm test.mpp --precompile