It occurs at compile time on an aggregate of a 2-dimensional packed array
type whose component type is itself a packed array, because the compiler
is trying to pack the intermediate aggregate and ends up rewriting a bunch
of subcomponents.  This optimization was originally devised for the case of
a scalar component type so the change adds this restriction.

gcc/ada/

	* exp_aggr.adb (Is_Two_Dim_Packed_Array): Return true only if the
	component type of the array is scalar.