Add the initial no-std Motor OS compiler target.
Motor OS has been developed for several years in the open:
https://github.com/moturus/motor-os.
It has a more or less full implementation of Rust std library,
as well as tokio/mio ports.
Build instructions can be found here:
https://github.com/moturus/motor-os/blob/main/docs/build.md.
Signed-off-by: U. Lasiotus <lasiotus@motor-os.org>
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