Remove unused fns/data and make fns static

Remove unused fns/data and make fns static

* src/comp.c (saved_sigset, helper_temp_output_buffer_setup):
Remove; unused.
* src/comp.c (logfile, helper_link_table):
* src/fns.c (hashfn_equal, hashfn_eql):
* src/frame.c (frame_windows_min_size):
* src/gnutls.c (emacs_gnutls_global_init):
* src/minibuf.c (Vcommand_loop_level_list):
* src/syntax.c (syntax_code_spec):
* src/timefns.c (time_overflow):
* src/xterm.c (x_xrender_color_from_gc_foreground)
(x_display_set_last_user_time):
Now static, since it’s not used elsewhere.
* src/xterm.c (x_xrender_color_from_gc_foreground)
(x_xrender_color_from_gc_background): Move earlier to avoid
forward use.
(x_xrender_color_from_gc_foreground): Do not define unless
!defined USE_CAIRO && (RENDER_MAJOR > 0 || RENDER_MINOR >= 2),
since it’s not used otherwise.