[llvm] [NFC][LLVM] Use namespace `Intrinsic` in `Intrinsics.cpp` (PR #114822)

[Alex MacLean via llvm-commits]

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

Seems reasonable to me, though I don't work on this file much

https://github.com/llvm/llvm-project/pull/114822