[Ada] Disallow Predicate_Failure without predicate

[Pierre-Marie de Rodat]

This patch checks RM-3.2.4(14.2/4), which requires Predicate_Failure to
be specified only on a subtype with a previous predicate specification
(for Static_Predicate or Dynamic_Predicate). We apply the same rule to
the GNAT-specific Predicate aspect.

Tested on x86_64-pc-linux-gnu, committed on trunk

gcc/ada/

	* sem_ch13.adb (Predicate_Failure): Check that the type has
	predicates.  Remove the setting of Has_Delayed_Aspects and
	Freeze_Node, because (if the code is legal) it should have
	already been done by the predicate aspect.
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