[Ada] Prevent overflow in computation of aggregate size

[Ada] Prevent overflow in computation of aggregate size

When computing size of a static aggregate to decide if it should be
transformed into assignments and loops we could have an overflow check.
This is mostly harmless, because colossal aggregates will likely crash
the application anyway, no matter how we transform them.

This was not detected because compiler was built with -gnatg switch that
suppresses overflow checks (they are only enabled by an explicit -gnato
switch).

gcc/ada/

	* exp_aggr.adb (Component_Count): Calculate size as an Uint and
	only then check if it is in the range of Int, as otherwise the
	multiplication of Int values can overflow.