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

[Valentin Clement バレンタイン クレメン via cfe-commits]

clementval wrote:

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

I can see language features in IDE like vscode being a good candidate. 

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