More missing _unlocked <stdio.h> functions.

Also simplify trivial one-liners like perror/puts/fputs, and clean up
fread/fwrite slightly.

Fix perror to match POSIX.

Add basic perror and *_unlocked tests.

Bug: N/A
Test: ran tests
Change-Id: I63f83c8e0c15c3c4096509d17421ac331b6fc23d