[clang] [flang] [flang][Frontend] Implement printing defined macros via -dM (PR #87627)

[Krzysztof Parzyszek via cfe-commits]

kparzysz wrote:

Is building LLVMSupport and maybe a few other components a barrier, or do they just not want to do that?

https://github.com/llvm/llvm-project/pull/87627