[llvm] Make llvm-strip not eat the .gnu_debuglink section (PR #78919)

[James Henderson via llvm-commits]

https://github.com/jh7370 approved this pull request.

The code change looks good to me. Before this can be merged, please tweak your PR title and description slightly, as this is used for the final commt message that is merged into main:

1) Add [llvm-objcopy] to the title line (llvm-strip is basically just an alias of llvm-objcopy with some slightly different command-line options and we tend to use the llvm-objcopy tag more often than llvm-strip).
2) The title should mention --strip-all, so something like `[llvm-objcopy] Don't remove .gnu_debuglink section with --strip-all`
3) In the description, make sure you're using the actual links to the issue, rather than the GitHub shorthand of #NNNNNN: this is because if somebody is looking at the git log on the command-line, #NNNNNN isn't a useful link.
4) In the description, mention llvm-objcopy as well as llvm-strip and --strip-all (e.g. "and therefore makes llvm-strip (and llvm-objcopy) not remove the .gnu_debuglink section when used with --strip-all"). Note that --strip-all is on by default for llvm-strip, but not llvm-objcopy, hence why the behaviour works as it does.

When you've made those changes, ping me and I'll merge the patch for you.

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