Change SKIP_GTK to SKIP_GTK2 in configure.
diff --git a/src/auto/configure b/src/auto/configure
index 9688efa..5e0e57a 100755
--- a/src/auto/configure
+++ b/src/auto/configure
@@ -7911,7 +7911,7 @@
 fi
 
 
-if test -z "$SKIP_ATHENA" -o -z "$SKIP_NEXTAW" -o -z "$SKIP_MOTIF" -o -z "$SKIP_GTK"; then
+if test -z "$SKIP_ATHENA" -o -z "$SKIP_NEXTAW" -o -z "$SKIP_MOTIF" -o -z "$SKIP_GTK2"; then
     cppflags_save=$CPPFLAGS
   CPPFLAGS="$CPPFLAGS $X_CFLAGS"
   for ac_header in X11/xpm.h X11/Sunkeysym.h