patch 7.4.2243
Problem:    Warning for assigning negative value to unsigned. (Danek Duvall)
Solution:   Make cterm_normal_fg_gui_color and _bg_ guicolor_T, cast to long_u
            only when an unsigned is needed.
diff --git a/src/proto/gui_mac.pro b/src/proto/gui_mac.pro
index ebe13f3..9b59f1f 100644
--- a/src/proto/gui_mac.pro
+++ b/src/proto/gui_mac.pro
@@ -78,7 +78,7 @@
 void gui_mch_menu_hidden(vimmenu_T *menu, int hidden);
 void gui_mch_draw_menubar(void);
 int gui_mch_get_lightness(guicolor_T pixel);
-long_u gui_mch_get_rgb(guicolor_T pixel);
+guicolor_T gui_mch_get_rgb(guicolor_T pixel);
 int gui_mch_get_mouse_x(void);
 int gui_mch_get_mouse_y(void);
 void gui_mch_setmouse(int x, int y);