Make --without-x compatible with --enable-gcc-warnings.

Make --without-x compatible with --enable-gcc-warnings.
* configure.ac: If both --without-x and --enable-gcc-warnings are
specified, use -Wno-unused-variable, -Wno-unused-but-set-variable
and -Wno-unused-but-set-parameter.
* src/font.c (register_font_driver): Move check under HAVE_WINDOW_SYSTEM.
* src/font.h (struct font_driver): Move draw, get_bitmap and free_bitmap
members under HAVE_WINDOW_SYSTEM.
* src/keyboard.c (make_lispy_focus_out): Likewise.
(record_menu_key): Move under HAVE_MENUS.
* src/xdisp.c (toplevel): Move hourglass_shown_p, hourglass_atimer and
THIN_SPACE_WIDTH under HAVE_WINDOW_SYSTEM.
(syms_of_xdisp): Adjust user.
(window_box_edges): Define only if HAVE_WINDOW_SYSTEM.
(start_hourglass, cancel_hourglass):
* src/xfaces.c (toplevel): Likewise with PT_PER_INCH,
clear_font_table_count, CLEAR_FONT_TABLE_COUNT
and CLEAR_FONT_TABLE_NFONTS.
(set_font_frame_param, clear_face_gcs, realize_non_ascii_face):
Declare only if HAVE_WINDOW_SYSTEM.
(lface_same_font_attributes_p, clear_face_gcs): Define only
if HAVE_WINDOW_SYSTEM.