[Ada] Spurious error on predicate of subtype in generic

[Ada] Spurious error on predicate of subtype in generic

This patch fixes a spurious error on a dynamic predicate of a record
subtype when the expression for the predicate includes a selected
component that denotes a component of the subtype.

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

gcc/ada/

	* sem_ch8.adb (Find_Selected_Component): If the prefix is the
	current instance of a type or subtype, complete the resolution
	of the name by finding the component of the type denoted by the
	selector name.

gcc/testsuite/

	* gnat.dg/predicate4.adb, gnat.dg/predicate4_pkg.ads: New
	testcase.

From-SVN: r272961