patch 8.2.0863: cannot set a separate color for underline/undercurl

Problem:    Cannot set a separate color for underline/undercurl.
Solution:   Add the t_AU and t_8u termcap codes. (Timur Celik, closes #6011)
diff --git a/src/globals.h b/src/globals.h
index 89aeb96..57577d4 100644
--- a/src/globals.h
+++ b/src/globals.h
@@ -485,9 +485,11 @@
 EXTERN int	cterm_normal_fg_color INIT(= 0);
 EXTERN int	cterm_normal_fg_bold INIT(= 0);
 EXTERN int	cterm_normal_bg_color INIT(= 0);
+EXTERN int	cterm_normal_ul_color INIT(= 0);
 #ifdef FEAT_TERMGUICOLORS
 EXTERN guicolor_T cterm_normal_fg_gui_color INIT(= INVALCOLOR);
 EXTERN guicolor_T cterm_normal_bg_gui_color INIT(= INVALCOLOR);
+EXTERN guicolor_T cterm_normal_ul_gui_color INIT(= INVALCOLOR);
 #endif
 #ifdef FEAT_TERMRESPONSE
 EXTERN int	is_mac_terminal INIT(= FALSE);  // recognized Terminal.app