'RELENG_5_3_0_RELEASE'.

This commit was manufactured to restore the state of the 5.3-RELEASE image.

in return value not in errno.

_thr_leave_cancellation_point to _thr_cancel_leave, add a parameter
to _thr_cancel_leave to indicate whether cancellation point should be
checked, this gives us an option to not check cancallation point if
a syscall successfully returns to avoid any leaks, current I have
creat(), open() and fcntl(F_DUPFD) to not check cancellation point
after they sucessfully returned.

Replace some members in structure kse with bit flags to same some
memory.

Conditionally compile THR_ASSERT to nothing if _PTHREAD_INVARIANTS is
not defined.

Inline some small functions in thr_cancel.c.

Use __predict_false in thr_kern.c for some executed only once code.

Reviewd by: deischen

yet, so we can protect some locking code from being interrupted by signal
handling. When KSE mode is turned on, reset the thread flag to scope process
except we are running in 1:1 mode which we needn't turn it off.
Also remove some unused member variables in structure kse.

Tested by: deischen

Reviewed by: deischen

  is system bound thread and when it is blocked, no upcall is generated.

o Add ability to libkse to allow it run in pure 1:1 threading mode,
  defining SYSTEM_SCOPE_ONLY in Makefile can turn on this option.

o Eliminate code for installing dummy signal handler for sigwait call.

o Add hash table to find thread.

Reviewed by: deischen

its waitset, but if the signal is not masked by the thread, the signal
can interrupt the thread and signal action can be invoked by the thread,
sigwait should return with errno set to EINTR.
Also save and restore thread internal state(timeout and interrupted)
around signal handler invoking.

outside of lock.

use [signal number - 1] as subscript to access the array.