Change the return type of the fallback implementation of the
atomic_compare_exchange_* macros in stdatomic.h to _Bool.
Remove redundant space.
Implement fdclosedir(3) function, which is equivalent to the closedir(3)
function, but returns directory file descriptor instead of closing it.

Submitted by:	Mariusz Zaborski <oshogbo@FreeBSD.org>
Sponsored by:	Google Summer of Code 2013