Re-define `__priority_which`s as c_uint in linux-gnu

src/unix/bsd/mod.rs

src/unix/haiku/mod.rs

src/unix/hermit/mod.rs

src/unix/linux_like/android/mod.rs

src/unix/linux_like/emscripten/mod.rs

src/unix/linux_like/linux/gnu/mod.rs

src/unix/linux_like/linux/musl/mod.rs

src/unix/mod.rs

src/unix/newlib/mod.rs

src/unix/redox/mod.rs

src/unix/solarish/mod.rs

src/unix/uclibc/mod.rs