[Ada] Support for local unix sockets in GNAT.Sockets API

[Ada] Support for local unix sockets in GNAT.Sockets API

Sock_Addr_Type has Family_Unix variant now. This variant can be created
with function Unix_Local_Addr call. And this variant is working in
GNAT.Socket routines where it is appropriate.

2019-09-17  Dmitriy Anisimkov  <anisimko@adacore.com>

gcc/ada/

	* gsocket.h: Include sys/un.h.
	* s-oscons-tmplt.c (AF_UNIX): New constant generation.
	(SIZEOF_sockaddr_un): Idem.
	* libgnat/g-socket.ads (Family_Type): New value Family_Unix
	added.
	(Family_Inet_4_6): New subtype only for network families.
	(Sock_Addr_Type): Add Unbounded_String field for Family_Unix
	variant.
	(Unix_Socket_Address): Create Sock_Addr_Type from socket
	pathname.
	(Network_Socket_Address): Create Sock_Addr_Type from
	Inet_Addr_Type and Port_Type parameters.
	* libgnat/g-socket.adb: Support local unix address in socket
	routines.
	(Get_Address_Info): Disable warning about Result may be
	referenced before it has a value. Remove duplicated code to exit
	from Look_For_Supported.
	* libgnat/g-sothco.ads (Unix_Name_Length): New constant defining
	maximum number of characters in local socket address path.
	(Sockaddr): Add variant for Family_Unix address family. Move
	Sin_Port and Sin_Family to Family_Inet section. Add Sin6_Port
	and Sin6_Family to Family_Inet6 section.
	(Set_Address): Add out parameter Length to return valuable
	Sockaddr data length.
	(Get_Address): Add input parameter Length to set valuable
	Sockaddr data length.
	* libgnat/g-sothco.adb: Support local unix address in socket
	routines.

From-SVN: r275770