patch 8.2.1878: GTK: error for redefining function

Problem:    GTK: error for redefining function. (Tony Mechelynck)
Solution:   Remove "gtk_" prefix from local functions and prepend "gui_" to
            global functions.
diff --git a/src/version.c b/src/version.c
index d18f101..78e4752 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1878,
+/**/
     1877,
 /**/
     1876,