[Ada] Code cleanup on functions inlining

[Ada] Code cleanup on functions inlining

This patch is preventive: it improves checks on inline functions that
return unconstrained type. It does not change the functionality of
the compiler.

2018-07-16  Javier Miranda  <miranda@adacore.com>

gcc/ada/

	* inline.adb (Build_Body_To_Inline): Minor code reorganization that
	ensures that calls to function Has_Single_Return() pass a decorated
	tree.
	(Has_Single_Return.Check_Return): Peform checks on entities (instead on
	relying on their characters).

From-SVN: r262708