extra-link-arg: support all link types

[davidhewitt]

This commit adds support for the remaining link types to -Zextra-link-arg:

rustc-link-arg-tests
rustc-link-arg-benches
rustc-link-arg-examples

This would be useful in PyO3, where users writing Python extension modules (which do link against libpython) want to run cargo tests for extension module. As executables, these tests need to link against libpython.

[rust-highfive]

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[ehuss]

Thanks for the PR!

One question I had is for examples. It looks like this only applies the flags for executable examples. I was wondering if it would make sense to also pass the flags for cdylib examples? Those are probably very rare, but that's the kind of thing that is difficult to change afterwards due to backwards compatibility.

Can you also update unstable.md with the new additions?

[bors]

☔ The latest upstream changes (presumably #9486) made this pull request unmergeable. Please resolve the merge conflicts.

[davidhewitt]

Sorry for the long delay, I hope to pick this PR up very soon.

I just saw #9562. Is that also relevant to these flags? It was looking potentially quite elegant for PyO3 to push these flags downstream automatically from its build.rs, but I think we can happily find alternative ways to help users add them in their own build.rs if needed.

[ehuss]

I'm gonna close this due to inactivity. Feel free to reopen or create a new PR when you've got time to work on this again. Thanks!