[llvm] [llvm][X86] REX profile for UEFI (PR #138362)

[Tristan Ross via llvm-commits]

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

LGTM, one of the next things I'd like to see happen is if we can fix lld-link to actually link a libc and start file for UEFI using LLVM libc. Currently, we have to manually supply the paths. Ideally, this should be done automatically.

https://github.com/llvm/llvm-project/pull/138362