ada: Fix long-standing issue with qualified expressions of class-wide types

ada: Fix long-standing issue with qualified expressions of class-wide types

Given the very specific name resolution rules for qualified expressions, the
Covers predicate cannot be used when the qualified expression is of a class-
wide type and, therefore, Analyze_Qualified_Expression needs to resort to a
stricter type compatibility analysis. But, unlike Covers, it fails to factor
out the limited views of the types, which may lead to spurious errors.

gcc/ada/ChangeLog:

	* sem_ch4.adb (Analyze_Qualified_Expression): For a class-wide type,
	check for an exact match modulo the Non_Limited_View attribute.