Allow injecting a profiler runtime into #![no_core] crates

[Zalathar]

An alternative to #133300, allowing -Cinstrument-coverage to be used with -Zbuild-std.

The incompatibility between profiler_builtins and #![no_core] crates appears to have been caused by profiler_builtins depending on core, and therefore conflicting with core (or minicore).

But that's a false dependency, because the profiler doesn't contain any actual Rust code. So we can just mark the profiler itself as #![no_core], and remove the incompatibility error.

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For context, the error was originally added by #79958.

[rustbot]

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[Zalathar]

cc @Enselic @jieyouxu

[jieyouxu]

I can't say I'm too familiar with profiler_builtins injection either, but cutting off the unnecessary dependency to core seems like a less fragile option than only skipping the profiler_builtins injection when building an .rlib.

[rustbot]

These commits modify the library/Cargo.lock file. Unintentional changes to library/Cargo.lock can be introduced when switching branches and rebasing PRs.

If this was unintentional then you should revert the changes before this PR is merged.
Otherwise, you can ignore this comment.

[Zalathar]

r? compiler

It's possible to write a run-make test that actually runs cargo with -Zbuild-std and RUSTFLAGS="-Cinstrument-coverage", but it's a bit fiddly and takes 20+ seconds to run (since it builds its own libraries), so I'm not sure whether it's worth adding.

[jieyouxu]

r? jieyouxu

[jieyouxu]

Thanks, this seems reasonable to me, just one nit. You can r=me with the nit.

[jieyouxu]

@rustbot author

[jieyouxu]

@bors rollup=never (profiler runtime setup modifications)

[Zalathar]

Addressed review feedback (diff).

@bors r=jieyouxu

[bors]

📌 Commit 6798eca has been approved by jieyouxu

It is now in the queue for this repository.