[lld] [LLD][COFF] Support marking sections as x86_64 code in ARM64EC object files (PR #135280)

[Martin Storsjö via llvm-commits]

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

LGTM. This is quite a tricky concept, especially wrt relocations being interpreted according to another standard. (Although that's only an issue with the yaml representation.) The implementation looks good!

https://github.com/llvm/llvm-project/pull/135280