Partially revert the fix for sem_ch13.adb as it does not comply
with RM 13.14(7.2/5).

gcc/ada/ChangeLog:

	* sem_ch13.adb (Check_Aspect_At_End_Of_Declarations): Restore calls
	to Preanalyze_Spec_Expression that were replaced by calls to
	Preanalyze_And_Resolve. Add documentation.
	(Check_Aspect_At_Freeze_Point): Ditto.