[Ada] Fix internal error on allocator with function call

[Ada] Fix internal error on allocator with function call

2018-05-31  Eric Botcazou  <ebotcazou@adacore.com>

gcc/ada/

	* gcc-interface/trans.c (Call_to_gnu): If this is a function call and
	there is no target, also create a temporary for the return value for
	an allocator if the type is an unconstrained record type with default
	discriminant.

From-SVN: r261007