Rewriting of boxes in record aggregates into the corresponding default
values was done in resolution, where we special-cased access types and
scalar types with a Default_Value aspect.

However, this rewriting rather belong to expansion. Also, the
special-casing didn't take Normalize_Scalars nor Initialize_Scalars
pragmas into account and it didn't work for private types.

Now the resolution keeps boxes that require simple initialization, while
expansion reuses existing routines for initialization of record types.

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

gcc/ada/

	* exp_aggr.adb (Initialize_Record_Component): Add assertion
	about one of the parameters, so that illegal attempts to
	initialize record components with Empty node are detected early
	on.
	(Build_Record_Aggr_Code): Handle boxes in aggregate component
	associations just the components with no initialization in
	Build_Record_Init_Proc.
	* sem_aggr.adb (Resolve_Record_Aggregate): For components that
	require simple initialization carry boxes from resolution to
	expansion.
	* sem_util.adb (Needs_Simple_Initialization): Remove redundant
	paren.