ada: Add mechanism to test internal error machinery

ada: Add mechanism to test internal error machinery

This patch adds a pragma that triggers an internal compiler error when
analyzed. It is not externally documented and makes it possible to test
the code that runs when the compiler encounters an internal error.

gcc/ada/ChangeLog:
	* snames.ads-tmpl: Add new pragma definition.
	* par-prag.adb (Prag): Handle new pragma.
	* sem_prag.adb (Analyze_Pragma): Implement new pragma.