[llvm] [llvm-objcopy] Don't remove .gnu_debuglink section when using --strip-all (PR #78919)

[Fangrui Song via llvm-commits]

MaskRay wrote:

> @felixkellenbenz, I've gone ahead and merged this. Please keep an eye out for test failure emails from the CI build bots that look like they might be to do with your change (note that you may get some failure emails that have nothing to do with your change - you can safely ignore those ones).

This commit has an author field of `xxx at users.noreply.github.com` and a committer field of `GitHub <noreply at github.com>`. Build bots cannot deal with this situation (technically it could leave a comment, but this is not implemented; and build bots have too high false positives right now..)

https://discourse.llvm.org/t/hidden-emails-on-github-should-we-do-something-about-it/74223

https://github.com/llvm/llvm-project/pull/78919