[Ada] Warning on nonmatching subtypes in fully conforming subprogram specs and bodies

[Ada] Warning on nonmatching subtypes in fully conforming subprogram specs and bodies

gcc/ada/

	* sem_ch6.adb: Add with and use of Warnsw.
	(Check_Conformance): Report a warning when subtypes or
	designated subtypes of formal parameters or result subtypes
	denote different declarations between the spec and body of the
	(Subprogram_Subtypes_Have_Same_Declaration): New function nested
	within Check_Conformance that determines whether two subtype
	entities referenced in a subprogram come from the same
	declaration. Returns True immediately if the subprogram is in a
	generic instantiation, or the subprogram is marked Is_Internal
	or is declared in an internal (GNAT library) unit, or GNAT_Mode
	is enabled, otherwise compares the nonlimited views of the
	entities (or their designated subtypes' nonlimited views in the
	anonymous access cases).
	(Nonlimited_View_Of_Subtype): New function nested within
	function Subprogram_Subtypes_Have_Same_Declaration that returns
	Non_Limited_View of a type or subtype that is an incomplete or
	class-wide type that comes from a limited of a
	package (From_Limited_With is True for the entity), or returns
	Full_View when the nonlimited view is an incomplete type.
	Otherwise returns the entity passed in.
	* warnsw.ads (Warn_On_Pedantic_Checks): New warning flag.
	(type Warning_Record): New component Warn_On_Pedantic_Checks.
	* warnsw.adb (All_Warnings): Set Warn_On_Pedantic_Checks from
	parameter Setting.
	(Restore_Warnings): Restore the value of the
	Warn_On_Pedantic_Checks flag.
	(Save_Warnings): Save the value of the Warn_On_Pedantic_Checks
	flag.
	(Set_Underscore_Warning_Switch): Add settings of the
	Warn_On_Pedantic flag according to the switch ("-gnatw_p" vs.
	"-gnatw_P").
	* doc/gnat_ugn/building_executable_programs_with_gnat.rst: Add
	documentation of new switches -gnatw_p and -gnatw_P (warnings
	for pedantic checks).
	* gnat_ugn.texi: Regenerate.
	* usage.adb: Add Warn_On_Pedantic_Checks.