[clang] [clang][Modules] Diagnose mismatching pcm dependencies in explicit buiilds (PR #137068)

[Jan Svoboda via cfe-commits]

https://github.com/jansvoboda11 approved this pull request.

LGTM, but I'd try to align the spelling of the diagnostic (`"-Wlazy-pcm-mismatch"`) with how we talk about the `-fmodule-file=X=X.pcm` option (`"mapping of module name to precompiled module file"`). Maybe `"-Wmodule-file-mapping-mismatch"` or something similar?

https://github.com/llvm/llvm-project/pull/137068