The wait3 function was removed in the 2001 edition of POSIX.
sys/wait.h wrongly declares it for the 2001 and 2008 editions of POSIX
when XSI features are enabled. This patch fixes the conditionals.
Tested for x86_64.
[BZ #21625]
* posix/sys/wait.h (strust rusage forward declaration): Change
[__USE_XOPEN_EXTENDED] conditional to [__USE_XOPEN_EXTENDED &&
!__USE_XOPEN2K].
(wait3): Likewise.