Use cbitset crate instead of custom bitset implementation in select

See merge request !221

Well I'm dumb... This test was already ran in a way that wasn't
verifying output, because this test outputs things that can
differ. Excuse me for not noticing!

This reverts commit 0af78b1e.

Rename __assert to __assert_fail

See merge request !212

Implement remaining LCG functions

See merge request !219

Implement posix_memalign()

See merge request !220

Fix out-of-bounds error in strsignal

See merge request !222

Make valloc() get page size through sysconf(), add tests

See merge request redox-os/relibc!216

Implement LCG pseudorandom number functions

See merge request redox-os/relibc!213

Add memrchr()

See merge request !214

Spring cleanup

See merge request redox-os/relibc!217

This makes relibc more compatible with other libc implementations

The race condition didn't trigger when I tested it, so I assumed I had
solved it...

Some recipes require the headers, but they don't explicitly say
so. Parallel make (-j`nproc`) might start compiling the libs when the
headers aren't done yet.