New command queue-signal.

New command queue-signal.

If I want to change the signalled state of multiple threads
it's a bit cumbersome to do with the "signal" command.
What you really want is a way to set the signal state of the
desired threads and then just do "continue".

This patch adds a new command, queue-signal, to accomplish this.
Basically "signal N" == "queue-signal N" + "continue".
That's not precisely true in that "signal" can be used to inject
any signal, including signals set to "nopass"; whereas "queue-signal"
just queues the signal as if the thread stopped because of it.
"nopass" handling is done when the thread is resumed which
"queue-signal" doesn't do.

One could add extra complexity to allow queue-signal to be used to
deliver "nopass" signals like the "signal" command.  I have no current
need for it so in the interests of incremental complexity, I have
left such support out and just have the code flag an error if one
tries to queue a nopass signal.

gdb/ChangeLog:

	* NEWS: Mention new "queue-signal" command.
	* infcmd.c (queue_signal_command): New function.
	(_initialize_infcmd): Add new queue-signal command.

gdb/doc/ChangeLog:

	* gdb.texinfo (Signaling): Document new queue-signal command.

gdb/testsuite/ChangeLog:

	* gdb.threads/queue-signal.c: New file.
	* gdb.threads/queue-signal.exp: New file.