(__lll_robust_lock_wait): Also set FUTEX_WAITERS bit if we got the
mutex.
(__lll_robust_timedlock_wait): Likewise.
* sysdeps/unix/sysv/linux/i386/i486/lowlevelrobustlock.S
(__lll_robust_lock_wait): Likewise.
(__lll_robust_timedlock_wait): Likewise.
* sysdeps/unix/sysv/linux/lowlevelrobustlock.c
(__lll_robust_lock_wait): Likewise.
(__lll_robust_timedlock_wait): Likewise.