gdb/testsuite/

	* boards/native-gdbserver.exp: Move invoke of
	process_multilib_options to gdbserver-base.exp.
	Move set_board_info 'compiler', 'gdb,noinferiorio',
	'gdb,nofileio', 'gdb_server_prog' and 'gdb,predefined_tsv' to
	gdbserver-base.exp.
	Move proc ${board}_download, ${board}_upload and
	${board}_file to gdbserver-base.exp.
	* boards/native-extended-gdbserver.exp: Likewise.
	* boards/native-stdio-gdbserver.exp: Likewise.
	* boards/gdbserver-base.exp: New file.