Remove libc from MSVC targets

[saethlin]

@ChrisDenton started working on a project to remove libc from Windows MSVC targets. I'm completing that work here.

The primary change is to cfg out the dependency in library/. And then there's a lot of test patching. Happy to separate this more if people want.

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[bors]

☔ The latest upstream changes (presumably #124084) made this pull request unmergeable. Please resolve the merge conflicts.

[bors]

☔ The latest upstream changes (presumably #124072) made this pull request unmergeable. Please resolve the merge conflicts.

[saethlin]

@ChrisDenton Is there anything else that needs to be done to remove libc from MSVC targets? I feel like this was almost too easy.

[ChrisDenton]

There's also #123976.

Also I found the std_detect crate is pulling in libc even if unused. See std uses the default features "std_detect_file_io", and "std_detect_dlsym_getauxval"

rust/library/sysroot/Cargo.toml

Line 14 in 0e15f5e

default = ["std_detect_file_io", "std_detect_dlsym_getauxval", "panic-unwind"]

Which in the std-detect crate enables the libc feature which in turn enables the libc dependency: https://github.com/rust-lang/stdarch/blob/7df81ba8c3e2d02c2ace0c5a6f4f32d800c09e56/crates/std_detect/Cargo.toml#L37

However, libc isn't used for those two features on Windows (it is currently used for a third, not default enabled. feature). But I'm not sure how to have a dependency enabled when it's both feature and target specific.

[ChrisDenton]

Rebasing on this PR and excluding libc from std_detect I'm still seeing the following UI test failures:

failures:
    [ui] tests\ui\attributes\unix_sigpipe\unix_sigpipe-inherit.rs
    [ui] tests\ui\attributes\unix_sigpipe\unix_sigpipe-not-used.rs#without_feature
    [ui] tests\ui\attributes\unix_sigpipe\unix_sigpipe-not-used.rs#with_feature
    [ui] tests\ui\attributes\unix_sigpipe\unix_sigpipe-sig_dfl.rs
    [ui] tests\ui\attributes\unix_sigpipe\unix_sigpipe-rustc_main.rs
    [ui] tests\ui\attributes\unix_sigpipe\unix_sigpipe-sig_ign.rs
    [ui] tests\ui\error-codes\E0259.rs
    [ui] tests\ui\feature-gates\rustc-private.rs
    [ui] tests\ui\foreign\foreign-fn-linkname.rs
    [ui] tests\ui\foreign\foreign2.rs
    [ui] tests\ui\imports\issue-37887.rs
    [ui] tests\ui\lint\unnecessary-extern-crate.rs
    [ui] tests\ui\meta\no_std-extern-libc.rs
    [ui] tests\ui\process\no-stdio.rs
    [ui] tests\ui\runtime\stdout-during-shutdown.rs
    [ui] tests\ui\wait-forked-but-failed-child.rs

[saethlin]

Ah-ha! That makes more sense.

[saethlin]

Now we should be down to

    [ui] tests\ui\foreign\foreign2.rs
    [ui] tests\ui\foreign\foreign-fn-linkname.rs
    [ui] tests\ui\runtime\stdout-during-shutdown.rs
    [ui] tests\ui\wait-forked-but-failed-child.rs

These tests are all pretty unix-y, but I'm going to educate myself a bit and see if there's a way to make a windows equivalent in some cases.

[bors]

☔ The latest upstream changes (presumably #124208) made this pull request unmergeable. Please resolve the merge conflicts.

[bors]

☔ The latest upstream changes (presumably #124560) made this pull request unmergeable. Please resolve the merge conflicts.

[saethlin]

@bors r=ChrisDenton

[bors]

📌 Commit 39ef149 has been approved by ChrisDenton

It is now in the queue for this repository.