Drop the Separate form of -fmodule-name X, -fprofile-remapping-file X, and -frewrite-map-file X.
To the best of my knowledge they are not used. Their conventional Joined forms (-fFOO=) should be used instead.
-fdebug-compilation-dir X is used in several places, e.g. chromium/infra/goma.
It is also advertised in http://blog.llvm.org/2019/11/deterministic-builds-with-clang-and-lld.html
(-fdebug-compilation-dir=X` was added in 10.0.0: 44e0daf16e6985eb44ea9a629402852dbff9cb0b)
So we keep it but make the EQ form canonical and the Separate form an alias.
Should the help text move the the now-canonical _EQ form?