ada: Fix selection of Finalize subprogram in untagged case

The newly introduced Finalizable aspect makes it possible to derive from
a type that is not tagged but has a Finalize primitive. This patch fixes
problems where overridings of the Finalize primitive were ignored.

gcc/ada/ChangeLog:

	* exp_ch7.adb (Make_Final_Call): Tweak search of Finalize primitive.
	* exp_util.adb (Finalize_Address): Likewise.