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 redox-os/relibc!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 redox-os/relibc!233