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

[Krzysztof Parzyszek via cfe-commits]

kparzysz wrote:

How is this code used outside of LLVM?  Why do people want to use _without_ LLVM?  Just curious.

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