Add a new gdbarch hook to report additional signal information.

Add a new gdbarch hook to report additional signal information.

This is a more general version of the existing handle_segmentation_fault
hook that is able to report information for an arbitrary signal, not
just SIGSEGV.

gdb/ChangeLog:

	* gdbarch.c: Regenerate.
	* gdbarch.h: Regenerate.
	* gdbarch.sh (report_signal_info): New method.
	* infrun.c (print_signal_received_reason): Invoke gdbarch
	report_signal_info hook if present.