[Ada] Small cleanup throughout CStand body

[Ada] Small cleanup throughout CStand body

2020-06-17  Eric Botcazou  <ebotcazou@adacore.com>

gcc/ada/

	* cstand.adb (Stloc): Change to a renaming.
	(Staloc): Likewise.
	(Build_Unsigned_Integer_Type): Remove Nam parameter, use local
	constants and do not call Make_Name.
	(Make_Dummy_Index): Use local constants.
	(Create_Standard): Pass the name of entities as parameter in
	calls to New_Standard_Entity and remove calls to Make_Name.
	Adjust calls to Build_Unsigned_Integer_Type.
	(Identifier_For): Use local constant.
	(Make_Component): Pass the name of the component as parameter
	in call to New_Standard_Entity and remove call to Make_Name.
	(Make_Formal): Likewise.  Rename Formal_Name parameter into
	Nam and use local constant.
	(Make_Name): Delete.
	(New_Operator): Use local constant.
	(New_Standard_Entity): Rename S parameter into Nam and build
	the name here.  Remove call to Make_Name.
	(Register_Float_Type): Pass the name of the type as parameter
	in call to New_Standard_Entity and remove call to Make_Name.