Backport #3537 to libc-0.2

[operutka]

Backporting changes from #3537 to fix the following errors when building Rust std on Linux uClibc targets.

error[E0599]: no method named `si_pid` found for struct `siginfo_t` in the current scope
   --> /home/operutka/.rustup/toolchains/nightly-2024-06-05-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/std/src/sys/pal/unix/process/process_unix.rs:870:33
    |
870 |             if unsafe { siginfo.si_pid() } == 0 {
    |                                 ^^^^^^ method not found in `siginfo_t`

error[E0599]: no method named `si_status` found for struct `siginfo_t` in the current scope
   --> /home/operutka/.rustup/toolchains/nightly-2024-06-05-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/std/src/sys/pal/unix/process/process_unix.rs:908:39
    |
908 |         let status = unsafe { siginfo.si_status() };
    |                                       ^^^^^^^^^ method not found in `siginfo_t`

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[operutka]

@JohnTitor the pull request has been removed from the merge queue due to some unrelated problems in the CI pipeline. Is there anything I can do to fix this?