Replace uses of fixed-width integer aliases with Rust types

src/fuchsia/mod.rs

src/unix/bsd/apple/b32.rs

src/unix/bsd/apple/b64.rs

src/unix/bsd/apple/mod.rs

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

src/unix/bsd/freebsdlike/freebsd/aarch64.rs

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

src/unix/bsd/freebsdlike/freebsd/freebsd11/mod.rs

src/unix/bsd/freebsdlike/freebsd/freebsd12/mod.rs

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

src/unix/bsd/freebsdlike/freebsd/powerpc64.rs

src/unix/bsd/freebsdlike/freebsd/x86.rs

src/unix/bsd/mod.rs

src/unix/bsd/netbsdlike/mod.rs

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

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

src/unix/notbsd/android/b32/mod.rs

src/unix/notbsd/android/b64/mod.rs

src/unix/notbsd/android/mod.rs

src/unix/notbsd/emscripten/mod.rs