rework cancellation for sigwait, sigtimedwait and sigwaitinfo

rework cancellation for sigwait, sigtimedwait and sigwaitinfo

sigtimedwait:
- provide __sigtimedwait_nocancel
- use __SYSCALL_SIGSET_T_SIZE instead of _NSIG / 8
- do not provide __sigtimedwait
- guard a section to avoid failure on archs if SI_TKILL/SI_USER are not defined
sigwaitinfo:
- simply use sigtimedwait since that handles cancellation already
sigwait:
- use non-cancellable functions (sigtimedwait, sigsuspend)
- get rid of code already done in __sigtimedwait_nocancel

Signed-off-by: Peter S. Mazinger <ps.m@gmx.net>
Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>