Unpin libc and update for FreeBSD/riscv support

[jrtc27]

Currently libc is pinned to 0.2.174 in a couple of places due to bytecodealliance/rustix#1496. Although that issue is currently open, the comments suggest that it has in fact been resolved. Either way, this needs to be dealt with, as sticking with an old version of the libc crate means that FreeBSD/riscv support remains broken, as that requires 0.2.176 (see rust-lang/libc#4688), and holding back all architectures in rust for the sake of a single low-tier one doesn't seem like the right balance (even if FreeBSD/riscv is also low-tier in this case, tier 1 architectures would surely want to not be stuck on an old libc crate).

[jrtc27]

The FIXMEs came in #145567 but I can't obviously find any tracking issues for that, nor a sign that someone is working on removing the pins. This kind of pin seems important enough that leaving it to FIXMEs buried in the Cargo.toml files seems ill-advised.

[Gelbpunkt]

comments suggest that it has in fact been resolved

Correct, rustix > 1.1.1 works fine on loongarch64. The libc version also breaks mips64(le) musl at the moment (though that is only tier 3).

[brad0]

If you bump it up please bump up to 0.2.177 for OpenBSD.