[lld] [LLD] [MinGW] Hook up --icf=safe to -opt:safeicf (PR #70037)

[Reid Kleckner via llvm-commits]

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

Looks good!

The 2017 comments predate the addrsig tracking mechanisms that @pcc implemented, so this change makes sense today.

https://github.com/llvm/llvm-project/pull/70037