ada: Couple of adjustments coming from aliasing considerations

ada: Couple of adjustments coming from aliasing considerations

The first adjustment is to the expansion of implementation types for array
types with peculiar index types, for which the aliased property set on the
component of the original type must be copied; the implicit base type also
needs to be properly marked if the implementation type is constrained.

The second adjustment is to selected types in the runtime, which need to
be marked with pragma Universal_Aliasing because of their special usage.

gcc/ada/

	* exp_pakd.adb (Create_Packed_Array_Impl_Type): For non-bit-packed
	array types, propagate the aliased property of the component.
	(Install_PAT): Set fields on the implicit base type of an array.
	* libgnat/a-stream.ads (private part): Add pragma Universal_Aliasing
	for Stream_Element.
	* libgnat/g-alleve.ads: Add pragma Universal_Aliasing for all the
	vector types.
	* libgnat/g-alleve__hard.ads: Likewise.