Set errno in alloc functions and add further tests

See merge request !205

Just a small step along the way to reduce the massive wall of spam
every time you compile.

This was done partly automagically with `cargo fix`. The rest was me
deleting or commenting out a bunch of variables. Hope nothing was
important...

https://github.com/BurntSushi/rust-memchr is supposed to be a whole
lot faster :)

Add POSIX strerror_r

See merge request redox-os/relibc!207

Changed while loops to for

See merge request redox-os/relibc!206

Changed while loops to for - https://gitlab.redox-os.org/redox-os/relibc/issues/128