[llvm] [llvm] use 64-bit types for result of getDwarfRegNum (NFC) (PR #109492)

[William G Hatch via llvm-commits]

willghatch wrote:

Closing this due to technicalities in figuring out how to make a PR stack.  Opened again as: https://github.com/llvm/llvm-project/pull/109494

https://github.com/llvm/llvm-project/pull/109492