ada: Direct attribute definition for constructors

ada: Direct attribute definition for constructors

This patch introduces the 'Constructor attribute and implements its direct
attribute definition syntax within subprogram specification. This new shorthand
avoids having to come up with an arbitrary subprogram name and to type out the
constructor aspect. Before, constructors where defined through the aspect
Constructor, which has been removed.

Furthermore, this patch prepares for the expansion of direct attribute
definitions to other attributes.

gcc/ada/ChangeLog:

	* errout.adb (Set_Msg_Node): Support N_Attribute_Reference and
	nodes that denotes direct attribute definitions.
	* exp_dbug.ads: Description for the encoding of direct attribute
	definitions as tick are hard to deal in entity names.
	* erroutc.adb
	(Set_Msg_Insertion_Name): Replace underscore between prefix and
	attribute name in direct attribute definitions; at this point we
	lost the semantic information of node type and we resort to match
	the string name as described in exp_dbug.adb.
	* exp_aggr.adb (Convert_To_Positional): Use Needs_Construction and
	Has_Default_Constructor.
	* exp_ch3.adb (Build_Record_Init_Proc)
	(Expand_N_Object_Declaration): Likewise.
	* exp_attr.adb (Expand_N_Attribute_Reference): Likewise.
	* exp_ch4.adb (Expand_N_Allocator): Likewise.
	* exp_ch6.adb
	(Prepend_Constructor_Procedure_Prologue): Use
	Is_Constructor_Procedure.
	(Make_Parent_Constructor_Call): Use
	Direct_Attribute_Definition_Name.
	* gen_il-fields.ads: Remove Constructor_List and Constructor_Name.
	* gen_il-gen-gen_entities.adb: Likewise.
	* einfo.ads (Needs_Construction): Add description.
	(Has_Delayed_Aspects): Adjust indentation.
	* par-ch13.adb (P_Attribute_Designators): Parse attribute
	designators.
	(P_Representation_Clause): Use P_Attribute_Designators.
	* par-ch6.adb (P_Subprogram): Support attribute designators in
	subprogram name.
	(Rewrites_Entity_If_Direct_Attribute_Def): Fix the specification
	node in case of direct attribute definitions.
	* par-endh.adb (Check_End, Same_Label): Likewise.
	* par.adb (P_Attribute_Designators): Specification.
	* sem_attr.adb (Analyze_Attribute): Error when using 'Constructor
	outside procedure specification.
	(Analyze_Attribute): Add error handling code.
	* sem_ch3.adb (Analyze_Aspect_Specifications): Likewise.
	* sem_ch6.adb (Analyze_Direct_Attribute_Definition): Handle direct
	attribute definitions. Add error handling code for the
	'Construction attribute and set constructor flags when necessary.
	(Analyze_Subprogram_Specification): Use
	Analyze_Direct_Attribute_Definition.
	* sem_util.adb (Direct_Attribute_Definition_Name): Name of
	entities created for direct attribute definitions. We emit an
	error if multiple attributes.
	(Is_Direct_Attribute_Subp_Spec): Helper to check whether a
	subprogram specification is a direct attribute definition.
	(Is_Constructor_Procedure): Helper to check whether a subprogram
	is a constructor procedure.
	(Has_Default_Constructor): Check whether the default constructor
	exists.
	(Default_Constructor): Not used anymore.
	(Parameter_Count): Likewise.
	(Process_End_Label): Get_Attribute_Reference_Name_String encodes
	also direct attribute definition end labels.
	* sem_util.ads: Likewise.
	* snames.ads-tmpl: Support for 'Constructor attribute.
	* snames.adb-tmpl (Is_Direct_Attribute_Definition_Name): Helper to
	check attributes allowed in direct attribute definitions.
	* aspects.ads: Remove constructor aspect.
	* sem_ch13.adb: Likewise.