2019-08-05  Richard Biener  <rguenther@suse.de>

	PR middle-end/91169
	* fold-const.c (get_array_ctor_element_at_index): Create
	offset_ints according to the sign of the index type and treat
	that as signed if it is obviously so.

	* gnat.dg/array37.adb: New testcase.

From-SVN: r274114