urcu: fix compat_futex_noasync()

This patch fix two critical problems in the compatibility fallback of
compact_futex_noasync():

1) compat_futex_cond is not bound to any @uaddr, it services all @uaddr,
   if you wakeup only one thread(pthread_cond_signal), the @uaddr of
   this waking thread and the @uaddr of the woken-up thread may be different.
   The woken-up thread will very probably go to sleep again
   because his own condition is not true.

   *And* this waking thread(FUTEX_WAKE) wake up NOTHING.

2) If the caller want to wake up all waiting threads, he will use INT_MAX
   for @val, and:
                for (i = 0; i < INT_MAX; i++)
                        pthread_cond_signal(&compat_futex_cond);
   becomes almost infinity loop.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>