[Ada] Ignore volatile restrictions in preanalysis

gcc/ada/

	* sem_util.adb (Is_OK_Volatile_Context): All references to
	volatile objects are legal in preanalysis.
	(Within_Volatile_Function): Previously it was wrongly called on
	Empty entities; now it is only called on E_Return_Statement,
	which allow the body to be greatly simplified.
1 file changed