[Ada] Freezing too strict in instances

[Ada] Freezing too strict in instances

Should_Freeze_Type is relaxed to only take the relevant case into
account (entities denoted by generic actual parameters as per
13.14(5/3), as well as profile of any subprograms named as per
13.14(10.2/4)), instead of being overly conservative wrt instances and
as a result, wrongly rejecting some legal code.

In practice this means we only need to worry about profile of
subprograms named as part of instances.

gcc/ada/

	* freeze.adb (Should_Freeze_Type): Fix handling of freezing in
	instances.