[Ada] Spurious error on discriminant of incomplete type

[Ada] Spurious error on discriminant of incomplete type

This patch corrects the conformance verification of discriminants to
provide symmetry between the analysis of incomplete and full view
discriminants. As a result, types of discriminants always resolve to the
proper view.

2019-07-10  Hristian Kirtchev  <kirtchev@adacore.com>

gcc/ada/

	* sem_ch6.adb (Check_Discriminant_Conformance): Use Find_Type to
	discover the type of a full view discriminant.

gcc/testsuite/

	* gnat.dg/incomplete7.adb, gnat.dg/incomplete7.ads: New testcase.

From-SVN: r273347