ada: Unbounded recursion on character aggregates with predicated component subtype

The compiler was recursing endlessly when analyzing an aggregate of
an array type whose component subtype has a static predicate and the
component expressions are static, repeatedly transforming the aggregate
first into a string literal and then back into an aggregate. This is fixed
by suppressing the transformation to a string literal in the case where
the component subtype has predicates.

gcc/ada/ChangeLog:

	* sem_aggr.adb (Resolve_Aggregate): Add another condition to prevent rewriting
	an aggregate whose type is an array of characters, testing for the presence of
	predicates on the component type.