[compiler-rt] [compiler-rt] Use mangled function names on ARM64EC (PR #137960)

[Martin Storsjö via llvm-commits]

mstorsjo wrote:

I added a couple other reviewers as well, in case they have comments on it, but this does look good to me - and in case the others have comments within a couple of days, we can probably merge this.

https://github.com/llvm/llvm-project/pull/137960