Rollup merge of #147000 - moturus:motor-os_stdlib_pr, r=tgross35

std: Add Motor OS std library port

Motor OS was added as a no-std Tier-3 target in
[PR 146848](rust-lang/rust#146848) as x86_64-unknown-motor.

This PR adds the std library for Motor OS.

While the PR may seem large, all it does is proxy
std pal calls to [moto-rt](https://crates.io/crates/moto-rt). Where there is some non-trivial
code (e.g. thread::spawn), it is quite similar, often
identical, to what other platforms do.

Author: matthiaskrgr