Add sigaltstack

See merge request !218

Clippy fixes

See merge request !223

This reverts commit b4c738eb.

Make errno thread local

See merge request redox-os/relibc!228

Move alloc tests to expected-output tests

See merge request redox-os/relibc!226

Use try_from in getpagesize(), add test

See merge request redox-os/relibc!225

Alloc functions cleanup

See merge request redox-os/relibc!224

Implement l64a()

See merge request redox-os/relibc!227

WIP mainly because we *should* use thread locals, but #[thread_local]
causes segfaults.