Special-case wildcard requests in ravenscar-thread.c

Special-case wildcard requests in ravenscar-thread.c

ravenscar-thread.c intercepts resume and wait target requests and
replaces the requested ptid with the ptid of the underlying CPU.
However, this is incorrect when a request is made with a wildcard
ptid.

This patch adds a special case to ravenscar-thread.c for
minus_one_ptid.  I don't believe a special case for process wildcards
is necessary, so I have not added that.

Joel's description explains the bug well:

At the user level, we noticed the issue because we had a test were
we insert a breakpoint one some code which is only run from, say,
CPU #2, whereas we unfortunately resumed the execution after having
stopped somewhere in CPU #1. As a result, we sent an order to resume
CPU #1, which starves CPU #2 forever, because the code in CPU #1
waits for some of the Ada tasks allocated to CPU #2 (and we never
reach our breakpoint either).

gdb/ChangeLog
2019-02-15  Tom Tromey  <tromey@adacore.com>

	* ravenscar-thread.c (ravenscar_thread_target::resume)
	(ravenscar_thread_target::wait): Special case wildcard requests.