A null array aggregate of Ada 2022 requires a conditional runtime check
that was inserted as an if-statement. While gigi can handle statements
inserted into a list of declarations, in GNATprove such a statement will
cause a crash. It is better to insert a conditional raise node, which is
properly handled by both gigi and GNATprove.

Tested on x86_64-pc-linux-gnu, committed on trunk

gcc/ada/

	* sem_aggr.adb (Resolve_Null_Array_Aggregate): Insert check as a
	Raise_Constraint_Error node and not an If_Statement.