Fix invalid memory reference in signal and sigaction

See merge request !239

The sigaction handler called map on an option, creating a pointer to a
move value. This in turned caused UB for signal handlers. Avoid using
pointers directly, and instead prefer references.

I didn't think it'd be this useful first, but thank god for `cargo fix --edition`!

Not sure if I should add a RwLock for the ptrace state too...

It's happening...

Fix cbindgen for disabled headers

See merge request !237

Remove defines that are generated by new cbindgen from bits

See merge request redox-os/relibc!234

Don't use diff on Redox

See merge request !233