[Ada] Add warning on redundant others_clause in array aggregate

[Ada] Add warning on redundant others_clause in array aggregate

This patch adds a warning on a redundant others_clause in an array aggregate
when all index positions are already specified in previous positional or named
associations. The warning is emitted when Warn_On_Redundant_Constructs is
enabled.

2018-05-24  Ed Schonberg  <schonberg@adacore.com>

gcc/ada/

	* exp_aggr.adb (Flatten): Add a warning on an others clause in an array
	aggregate with static bounds when named associations cover all index
	positions and the others clause is redundant.

gcc/testsuite/

	* gnat.dg/others1.adb: New testcase.

From-SVN: r260657