[llvm] [RegAllocFast] fold foldable inline asm (PR #74344)

[via llvm-commits]

qcolombet wrote:

> Long term I still think some better integration into the spilling code is desirable; but I guess I could live with the pessimistic codegen for now.

FWIW, right now because of how we lower the inline asm constraints, we always have the pessimistic codegen.
So I would actually be fine if it was just what we support.

https://github.com/llvm/llvm-project/pull/74344