[llvm] [DirectX] Infrastructure to collect shader flags for each function (PR #112967)

[Damyan Pepper via llvm-commits]

https://github.com/damyanp requested changes to this pull request.

I stopped reading this after seeing the string construction in the comparison function.  I'm either missing something big about this change, which means I'd need to review again once I've been corrected, or this PR is going to be somewhat different anyway, so I'll wait until that's resolved before looking at it again.

https://github.com/llvm/llvm-project/pull/112967