[llvm] [TableGen] Efficiency improvements for encoding HwMode collection. (PR #82902)

[Jason Eckhardt via llvm-commits]

nvjle wrote:

I hope one of @topperc @jyknight @jmolloy @0x59616e @wangpc-pp (based on recent commits or past reviews to the same general area) might review this small patch, thank you.

https://github.com/llvm/llvm-project/pull/82902