[lld] [LLD][COFF] add __lld_buildid symbol. (PR #74652)

[Reid Kleckner via llvm-commits]

rnk wrote:

> Can we avoid `lld` in the name and call it just `__buildid`? I'm worried that calling it `__lld_buildid` might discourage other COFF linkers from adopting it.

That's reasonable. Can we make the name even more descriptive to reduce the risk of symbol conflicts? There are many implementers in the implementer's namespace (`__`). One idea: `__buildid_guid` `__build_guid` (it is a GUID, isn't it?).

https://github.com/llvm/llvm-project/pull/74652