[Ada] Spurious error with static predicate in generic unit

[Ada] Spurious error with static predicate in generic unit

This patch fixes a spurious error in a generic unit that invludes a
subtype with a static predicate, when the type is used in a case
expression.

2019-07-03  Ed Schonberg  <schonberg@adacore.com>

gcc/ada/

	* sem_ch13.adb (Build_Predicate_Functions): In a generic context
	we do not build the bodies of predicate fuctions, but the
	expression in a static predicate must be elaborated to allow
	case coverage checking within the generic unit.
	(Build_Discrete_Static_Predicate): In a generic context, return
	without building function body once the
	Static_Discrete_Predicate expression for the type has been
	constructed.

gcc/testsuite/

	* gnat.dg/predicate6.adb, gnat.dg/predicate6.ads: New testcase.
	* gnat.dg/static_pred1.adb: Remove expected error.

From-SVN: r272974