Adding UTIME_NOW and UTIME_OMIT to OSes which support utimensat

src/unix/bsd/apple/mod.rs

src/unix/bsd/freebsdlike/freebsd/mod.rs

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

src/unix/haiku/mod.rs

src/unix/solarish/mod.rs

src/wasi.rs