middle-end/101292 - invalid memory access with warning control

middle-end/101292 - invalid memory access with warning control

The warning control falls into the C++ trap of using a reference
to old hashtable contents for a put operation which can end up
re-allocating that before reading from the old freed referenced to
source.  Fixed by introducing a temporary.

2022-01-17  Richard Biener  <rguenther@suse.de>

	PR middle-end/101292
	* diagnostic-spec.c (copy_warning): Make sure to not
	reference old hashtable content on possible resize.
	* warning-control.cc (copy_warning): Likewise.