[clang] [C++20] [Modules] Introduce -fskip-odr-check-in-gmf (PR #79959)

[David Blaikie via cfe-commits]

dwblaikie wrote:

I'd still idly vote against adding this flag/support - but if other modules contributors feel it's the right thing to do, I won't stand in the way.

https://github.com/llvm/llvm-project/pull/79959