[lld] [LLD][COFF] Replace ARM64EC TLS symbols with native symbols when available (PR #212845)

[Jacek Caban via llvm-commits]

cjacek wrote:

I noticed one more problem with _tls_start and _tls_end symbols. Those really need to be merged, there may be only one real start and end. This also explains the merging behavior I mentioned earlier: for those we really want to make sure that the unused copy is not emitted.

With that logic in place, _tls_used and _tls_index may be just more of the same (just two more lines with this implementation), so I guess simplicity may be an argument for that... I would suggest starting with this PR, because we need it for _tls_start and _tls_end anyway, and follow-up with the robuster version.

https://github.com/llvm/llvm-project/pull/212845