Use the replacement source instead of the original source when generating -C metadata and -C extra-filename

[P-E-Meunier]

What does this PR try to resolve?

This commit fixes an issue when replacing two different sources with the same local one (for example using cargo vendor), where rustc errs saying that two types "defined at the same place in the same file" are "different".

See #14821.

How should we test and review this PR?

Use the steps described in #14821.

Additional information

This is really useful in the context of private registries and vendored dependencies.

[rustbot]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @epage (or someone else) some time within the next two weeks.

Please see the contribution instructions for more information. Namely, in order to ensure the minimum review times lag, PR authors and assigned reviewers should ensure that the review label (S-waiting-on-review and S-waiting-on-author) stays updated, invoking these commands when appropriate:

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[epage]

To help us track this, #14729 hasn't been accepted yet

(we generally ask for issues to be accepted before posting PRs, see https://doc.crates.io/contrib/process/index.html)

[P-E-Meunier]

Oops, I meant #14821, which is an issue. I updated the initial report.

[P-E-Meunier]

These two PRs are independent, one is for cargo vendor, the other one for cargo build. Any of them would already improve the situation and remove hacky workarounds in our workflow.