[llvm] [llvm] Use StringRef::{starts,ends}_with (NFC) (PR #74956)

[Simon Pilgrim via llvm-commits]

https://github.com/RKSimon approved this pull request.

LGTM - I couldn't see any clang-format warnings that were particularly severe (just code alignment etc.) - its up to you if you format them or not.

https://github.com/llvm/llvm-project/pull/74956