ada: Formal_Derived_Type'Size is not static

ada: Formal_Derived_Type'Size is not static

In deciding whether a Size attribute reference is static, the compiler could
get confused about whether an implicitly-declared subtype of a generic formal
type is itself a generic formal type, possibly resulting in an assertion
failure and then a bugbox.

gcc/ada/

	* sem_attr.adb (Eval_Attribute): Expand existing checks for
	generic formal types for which Is_Generic_Type returns False. In
	that case, mark the attribute reference as nonstatic.