musl: add semid_ds and seminfo

[JustSoup312]

Description

Adds the semid_ds and seminfo structs to musl. These exist in the musl C library, but are not wrapped in the libc crate yet.

Sources

• semid_ds: https://github.com/bminor/musl/blob/8fd5d031876345e42ae3d11cc07b962f8625bc3b/arch/generic/bits/sem.h
• seminfo: https://github.com/bminor/musl/blob/8fd5d031876345e42ae3d11cc07b962f8625bc3b/include/sys/sem.h

Checklist

• [x] Relevant tests in libc-test/semver have been updated
• [x] No placeholder or unstable values like *LAST or *MAX are included (see #3131)
• [x] Tested locally (cd libc-test && cargo test --target mytarget); especially relevant for platforms that may not be checked in CI

@rustbot label +stable-nominated

[tgross35]

@JustSoup312 gentle ping, are you able to get this over the line? Or do you need any help figuring something out?

[tgross35]

@JustSoup312 another gentle ping here