Add pthread mutex type constants

src/unix/bsd/apple/mod.rs

src/unix/bsd/freebsdlike/mod.rs

src/unix/bsd/openbsdlike/bitrig.rs

src/unix/bsd/openbsdlike/netbsd.rs

src/unix/bsd/openbsdlike/openbsd.rs

src/unix/notbsd/android/mod.rs

src/unix/notbsd/linux/mod.rs

src/unix/solaris/mod.rs