Check for the case where a user writes "in" instead of "of" in an
aggregate like "[for E in Some_Array when Some_Filter (E) => E]".

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

gcc/ada/

	* sem_aggr.adb
	(Resolve_Array_Aggregate): Generate an appropriate error message
	in the case where an error in the source code leads to an
	N_Iterated_Element_Association node in a bad context.