patch 8.0.0755: terminal window does not have colors in the GUI

Problem:    Terminal window does not have colors in the GUI.
Solution:   Lookup the GUI color.
diff --git a/src/proto/gui_x11.pro b/src/proto/gui_x11.pro
index 1e4410e..e490d0c 100644
--- a/src/proto/gui_x11.pro
+++ b/src/proto/gui_x11.pro
@@ -25,6 +25,7 @@
 int fontset_height(XFontSet fs);
 int fontset_height2(XFontSet fs);
 guicolor_T gui_mch_get_color(char_u *name);
+guicolor_T gui_mch_get_rgb_color(int r, int g, int b);
 void gui_mch_set_fg_color(guicolor_T color);
 void gui_mch_set_bg_color(guicolor_T color);
 void gui_mch_set_sp_color(guicolor_T color);