Refactor OpenBSD-like module into OpenBSD

libc-test/build.rs

src/unix/bsd/netbsdlike/mod.rs

src/unix/bsd/netbsdlike/openbsd/aarch64.rs

src/unix/bsd/netbsdlike/openbsd/mod.rs

src/unix/bsd/netbsdlike/openbsd/x86.rs

src/unix/bsd/netbsdlike/openbsd/x86_64.rs

src/unix/bsd/netbsdlike/openbsdlike/openbsd/mod.rs