[Ada] Fix expansion of quantified expressions as part of "others" associations

[Ada] Fix expansion of quantified expressions as part of "others" associations

2018-05-25  Ed Schonberg  <schonberg@adacore.com>

gcc/ada/

	* exp_aggr.adb (Flatten): A quantified expression cannot be duplicated
	in an others clause to prevent visibility issues with the generated
	loop variable.
	(Component_OK_For_Backend): Return false for a quantified expression.
	(Check_Static_Component): Ditto.

From-SVN: r260737