[Ada] Fix internal error on untagged record type with equality operator

[Ada] Fix internal error on untagged record type with equality operator

After the binding interpretation issued under AI12-0413, a user-defined
primitive equality operator of an untagged record type hides the predefined
equality operator in an instantiation, but this does not apply if the
instantiation appears in the same declarative region as the type and
before the declaration of this user-defined operator.

gcc/ada/

	* sem_res.adb (Resolve_Equality_Op): Make sure that the user-defined
	operator of an untagged record type is declared ahead of an instance
	before using it to resolve the equality operator in the instance.