[llvm] Minor optimizations to DW_OP_LLVM_extract_bits_* (PR #163812)

[J. Ryan Stinnett via llvm-commits]

jryans wrote:

I'll be travelling the first few days next week... Assuming no other feedback, I'll plan to merge this Thursday (23 Oct).

https://github.com/llvm/llvm-project/pull/163812