Try to replace the add_options_page
line with the following:
add_menu_page( 'Global Custom Options', 'Global Custom Options', 'manage_options', 'functions','global_custom_options' );
Try to replace the add_options_page
line with the following:
add_menu_page( 'Global Custom Options', 'Global Custom Options', 'manage_options', 'functions','global_custom_options' );