[llvm] X86: Add prefetch insertion based on Propeller profile (PR #166324)

[Simon Pilgrim via llvm-commits]

https://github.com/RKSimon requested changes to this pull request.

blanket clang-format makes it difficult to see the bones of this patch - and there are very few useful comments and descriptions on what is going on

https://github.com/llvm/llvm-project/pull/166324