[Ada] Fix runtime stack overflow for out/in-out actuals without discr.

[Ada] Fix runtime stack overflow for out/in-out actuals without discr.

2018-12-11  Javier Miranda  <miranda@adacore.com>

gcc/ada/

	* exp_aggr.adb (Convert_To_Assignments): When gnerating C, do
	not declare a temporary to initialize an aggregate assigned to
	Out or In_Out parameters whose type has no discriminants. This
	avoids stack overflow errors at runtime.

From-SVN: r266988