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.

Add completely untested redox epoll implementation

See merge request redox-os/relibc!211

Implement rand_r(), strnlen_s(), tempnam(), tmpnam()

See merge request redox-os/relibc!210

Handle zero len for strerror_r

See merge request redox-os/relibc!209

Resolve "BufferedVaList::index may read out of bounds"

Closes #140

See merge request redox-os/relibc!208