ada: Fix crash caused by missing New_Copy_tree

ada: Fix crash caused by missing New_Copy_tree

Since a recent refactor ("Factor common processing in expansion of
aggregates") where Initialize_Array_Component and
Initialize_Record_Component are merged, the behavior has slightly
changed. In the case of the expansion of an aggregate initialization
where the number of 'others' components is <= 3, the initialization
expression is not duplicated anymore, causing some incorrect multiple
definition when said expression is later transformed with
Expressions_With_Action that declares an object. The simple fix is to
add the now missing New_Copy_Tree where the assignments are created.

gcc/ada/

	* exp_aggr.adb (Build_Array_Aggr_Code) <Gen_Loop>: Copy the
	initialization expression when unrolling the loop.