Fix infinite loop in check_pf (BZ #12926)

The recvmsg could return 0 under some conditions and cause the
make_request function to be stuck in an infinite loop.

Thank you Jim King <jim.king@simplivity.com> for posting Paul's patch
on the list.
conformtest: clean up POSIX expections for sys/utsname.h, sys/wait.h.

Continuing the series of patches to clean up conformtest expectations
for "POSIX" (1995/6) based on review of the expectations against the
standard, this patch cleans up expectations for sys/utsname.h and
sys/wait.h.  Tested x86_64; a new XFAIL for sys/wait.h is added.

	* conform/data/sys/utsname.h-data (*_t): Allow.
	* conform/data/sys/wait.h-data [POSIX] (uid_t): Do not define.
	[POSIX] (WEXITED): Do not expect constant.
	[POSIX] (WSTOPPED): Likewise.
	[POSIX] (WNOHANG): Likewise.
	[POSIX] (WNOWAIT): Likewise.
	[POSIX] (siginfo_t): Do not expect type or elements.
	[POSIX] (pid_t): Do not expect type.
	[POSIX] (signal.h): Do not allow header.
	[POSIX] (sys/resource.h): Likewise.
	[POSIX] (si_*): Do not allow pattern.
	[POSIX] (W*): Likewise.
	[POSIX] (P_*): Likewise.
	[POSIX] (BUS_*): Likewise.
	[POSIX] (CLD_*): Likewise.
	[POSIX] (FPE_*): Likewise.
	[POSIX] (ILL_*): Likewise.
	[POSIX] (POLL_*): Likewise.
	[POSIX] (SEGV_*): Likewise.
	[POSIX] (SI_*): Likewise.
	[POSIX] (TRAP_*): Likewise.
	* conform/Makefile (test-xfail-POSIX/sys/wait.h/conform): New
	variable.