Support Redox OS libc for cross compilation #23905
Description
It seems like Redox will not have a stable syscall ABI, but will have a stable libc ABI through relibc. This should be straightforward for us to support with the usual libc-abi-tools approach.
We'd also need to plumb support through other places since this would be a new std.Target.Os.Tag tag. But I expect it all to be relatively straightforward.
Note that relibc is not stable yet, nor has Redox hit 1.0, so this is a project for the future.