[Ada] Fix link from body protected entry implementation to source code

[Ada] Fix link from body protected entry implementation to source code

gcc/ada/

	* einfo.ads: Move Corresponding_Protected_Entry...
	* sinfo.ads: ... here.
	* exp_ch9.adb (Build_Entry_Body): Link procedure and entry
	bodies.
	* gen_il-fields.ads (Opt_Field_Enum): Add
	Corresponding_Entry_Body field to nodes; remove
	Corresponding_Protected_Entry field from entities.
	* gen_il-gen-gen_entities.adb (Gen_Entities): Remove
	Corresponding_Protected_Entry field from E_Void and
	E_Subprogram_Body.
	* gen_il-gen-gen_nodes.adb (Gen_Nodes): Add
	Corresponding_Entry_Body field to N_Subprogram_Body.
	* sem_ch6.adb (Analyze_Subprogram_Specification): Remove
	manipulation of Ekind and Corresponding_Protected_Entry added as
	part of the support for varsize-nodes.