patch 8.1.0006: syn_id2cterm_bg() may be undefined

Problem:    syn_id2cterm_bg() may be undefined. (Axel Bender)
Solution:   Adjust #ifdef.
diff --git a/src/syntax.c b/src/syntax.c
index bb695b5..5feaac6 100644
--- a/src/syntax.c
+++ b/src/syntax.c
@@ -9854,7 +9854,9 @@
 }
 #endif
 
-#if defined(FEAT_TERMINAL) || defined(PROTO)
+#if (defined(WIN3264) \
+	&& !defined(FEAT_GUI_W32) \
+	&& defined(FEAT_TERMGUICOLORS)) || defined(PROTO)
     void
 syn_id2cterm_bg(int hl_id, int *fgp, int *bgp)
 {
diff --git a/src/version.c b/src/version.c
index a3eb91a..4093a8c 100644
--- a/src/version.c
+++ b/src/version.c
@@ -762,6 +762,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    6,
+/**/
     5,
 /**/
     4,