[Ada] Allow for GNATprove specific versions of routines from Sem_Disp

[Ada] Allow for GNATprove specific versions of routines from Sem_Disp

2018-05-28  Claire Dross  <dross@adacore.com>

gcc/ada/

	* sem_disp.ads, sem_disp.adb (Inheritance_Utilities): Package for
	generic inheritance utilities.
	(Generic_Inherited_Subprograms): Generic version of
	Inherited_Subprograms, generic in Find_Dispatching_Type function.
	(Generic_Is_Overriding_Subprogram): Generic version of
	Is_Overriding_Subprogram, generic in Find_Dispatching_Type function.
	(Inherited_Subprograms): Instance of Generic_Inherited_Subprograms with
	Sem_Disp.Find_Dispatching_Type.
	(Is_Overriding_Subprogram): Instance of
	Generic_Is_Overriding_Subprogram with Sem_Disp.Find_Dispatching_Type.
	(Inheritance_Utilities_Inst): Instance of Inheritance_Utilities
	with Sem_Disp.Find_Dispatching_Type.

From-SVN: r260835