Enqueue signal even when resuming threads

Enqueue signal even when resuming threads

Nowadays, we only enqueue signal when we leave thread pending in
linux_resume_one_thread.  If lwp->resume->sig isn't zero (GDB wants
to resume with signal), we pass lwp->resume->sig to
linux_resume_one_lwp.

In order to reduce the difference between resuming thread with signal
and proceeding thread with signal, when we resume thread, we can
enqueue signal too, and proceed thread.  The signal will be consumed in
linux_resume_one_lwp_throw from lwp->pending_signals.

gdb/gdbserver:

2016-07-21  Yao Qi  <yao.qi@linaro.org>

	* linux-low.c (proceed_one_lwp): Declare.
	(linux_resume_one_thread): Remove local variable 'step'.
	Lift code enqueue signal.  Call proceed_one_lwp instead of
	linux_resume_one_lwp.