Use const char* instead of char*.

Use const char* instead of char*.
* src/xterm.c (x_create_toolkit_scroll_bar):
* src/xfont.c (xfont_list_pattern):
* src/xfns.c (x_default_scroll_bar_color_parameter)
(xic_create_fontsetname, x_default_font_parameter)
(x_screen_planes):
* src/xdisp.c (c_string_pos, number_of_chars, reseat_to_string)
(store_mode_line_string, decode_mode_spec, display_string):
* src/menu.c (digest_single_submenu):
* src/keymap.h (initial_define_key, initial_define_lispy_key):
* src/keymap.c (initial_define_key, initial_define_lispy_key):
* src/image.c (image_error, image_keyword):
* src/gtkutil.h (xg_create_widget, xg_create_scroll_bar):
* src/gtkutil.c (xg_create_widget, xg_create_scroll_bar):
* src/ftfont.c (struct fc_charset_table, ftfont_spec_pattern)
(ftfont_list, ftfont_match):
* src/frame.c (frame_parm_table):
* src/font.h (font_intern_prop, font_parse_xlfd, font_parse_fcname)
(font_unparse_fcname, font_unparse_fcname, font_open_by_name)
(font_add_log, font_deferred_log):
* src/font.c (font_intern_prop, font_parse_xlfd, font_parse_fcname)
(font_unparse_fcname, font_unparse_fcname, font_open_by_name)
(font_add_log, font_deferred_log):
* src/emacs.c (argmatch):
* src/dispextern.h (struct it):
* src/coding.c (ENCODE_DESIGNATION):
* src/charset.c (define_charset_internal): Use const.