[clang] [clang] Avoid re-evaluating field bitwidth (PR #117732)

[Timm Baeder via cfe-commits]

tbaederr wrote:

I was hoping that saving the value as an `unsigned` directly would give a little more speedup.

`ConstantExpr` version: http://llvm-compile-time-tracker.com/compare.php?from=5a7b79c93e2e0c71aec016973f5f13d3bb2e7a62&to=a55efb0b221e7ea54b8f7c0e3f975c19a54e5796&stat=instructions:u

This version: http://llvm-compile-time-tracker.com/compare.php?from=6f16a8bf17ac9a171b5435ee53c3d2bef657bdad&to=6a1c51fd8b6b1d04294eaac65b261bedb451f22b&stat=instructions:u

So, you know... barely any difference in both cases I guess.

https://github.com/llvm/llvm-project/pull/117732