newlib: Fix ambiguous glob exports and other warnings for Vita and 3DS

[pheki]

Description

This is actually a followup of #4811. It turns out that it accidentally introduced an ambiguous glob export for _SC_PAGESIZE and _SC_GETPW_R_SIZE_MAX. After updating newlib, rustc is fails to compile for these targets as it can't resolve _SC_PAGESIZE here: https://github.com/rust-lang/rust/blob/5325015e29874334003d33d77b295d57f593f06a/library/std/src/sys/pal/unix/os.rs#L530-L532

While checking, I realized there were also other warnings, for many newlib structures that ended up being unused, which I fixed:

hostent definitions:

1. src/unix/mod.rs: The only actually resolved by rustc, and the most similar to newlib since at least 2017

2. src/unix/newlib/mod.rs: This one has been there since the start of the newlib module, which matched the 3DS upstream definition at the time. Since then, Revise network definitions for HorizonOS #3863 arrived removing the 3DS (horizon) from that definition as the upstream header had been updated.

3. src/unix/newlib/horizon/mod.rs: This one is the new correct definition for horizon, which was deliberately added in Revise network definitions for HorizonOS #3863 but is not being used as it's shadowed by 1.. I updated 1. so this definition will now be used.

pollfd

The definition in src/unix/mod.rs is the one being used and it matches with upstream newlib and the vita.

The definition in src/unix/newlib/mod.rs was unused but it matches with the 3ds headers, so I moved it into horizon and opted it out from the above.

unix::newlib::generic::{sigset_t, stat, dirent}

All unused as they were shadowed by vita's own definitions. Same goes for horizon except for dirent.

Sources

• newlib hostent: https://github.com/bminor/newlib/blob/f49f54b00d80ec12d6875def9252afba37f51825/newlib/libc/sys/rtems/include/netdb.h#L106-L113
• vita hostent: https://github.com/vitasdk/newlib/blob/11c38129967fe2f8893d24dd7742b6ed6bd54d5f/newlib/libc/sys/vita/include/netdb.h#L40-L46
• horizon hostent: https://github.com/devkitPro/libctru/blob/00760077a8418284554980290e20f85231c69c2b/libctru/include/netdb.h#L11-L17
• newlib pollfd: https://github.com/bminor/newlib/blob/f49f54b00d80ec12d6875def9252afba37f51825/newlib/libc/sys/rtems/include/sys/poll.h#L51-L55
• vita pollfd: https://github.com/vitasdk/newlib/blob/11c38129967fe2f8893d24dd7742b6ed6bd54d5f/newlib/libc/sys/vita/sys/poll.h#L49-L53
• horizon pollfd: https://github.com/devkitPro/libctru/blob/00760077a8418284554980290e20f85231c69c2b/libctru/include/poll.h#L12-L17

Checklist

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

Checked locally using cargo +nightly check --target {target} -Z build-std=core for:

• armv7-sony-vita-newlibeabihf: No warnings
• armv6k-nintendo-3ds: No warnings
• armv7-rtems-eabihf: Only an unused import warning on src/new/mod.rs: pub(crate) use rtems::*;

@rustbot label +stable-nominated

[pheki]

Pinging @Meziu as you as you're the 3DS maintainer who worked on #3863, in case you're available to help validating these changes