This patch adds a check on an iterator over a GNAT-specific formal container,
when the iterator specification includes a subtype indication that must be
compatible with the element type of the container.

2018-05-23  Ed Schonberg  <schonberg@adacore.com>

gcc/ada/

	* sem_ch5.adb (Analyze_Iterator_Specification): If a subtype indication
	is present, verify its legality when the domain of iteration is a
	GNAT-specific formal container, as is already done for arrays and
	predefined containers.

gcc/testsuite/

	* gnat.dg/iter1.adb, gnat.dg/iter1.ads: New testcase.

From-SVN: r260587