[llvm] [TableGen][CodeGen] Give every leaf register a unique regunit (PR #139526)

[Vikash Gupta via llvm-commits]

vg0204 wrote:

Its better than this #139206, as mine patch is unnecessarily creating a regUnit for non-leaf register, in case if its alias, but here that's avoided innately.

https://github.com/llvm/llvm-project/pull/139526