patch 8.1.0391: building in a shadow directory fails

Problem:    Building in a shadow directory fails.
Solution:   Don't link the xdiff directory but what's in it. (closes #3428)
diff --git a/src/Makefile b/src/Makefile
index b0747c8..9c19281 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -2765,7 +2765,7 @@
 
 shadow:	runtime pixmaps
 	$(MKDIR_P) $(SHADOWDIR)
-	cd $(SHADOWDIR); ln -s ../*.[chm] ../*.in ../*.sh ../*.xs ../*.xbm ../gui_gtk_res.xml ../toolcheck ../proto ../xdiff ../libvterm ../vimtutor ../gvimtutor ../install-sh ../Make_all.mak .
+	cd $(SHADOWDIR); ln -s ../*.[chm] ../*.in ../*.sh ../*.xs ../*.xbm ../gui_gtk_res.xml ../toolcheck ../proto ../libvterm ../vimtutor ../gvimtutor ../install-sh ../Make_all.mak .
 	mkdir $(SHADOWDIR)/auto
 	cd $(SHADOWDIR)/auto; ln -s ../../auto/configure .
 	$(MKDIR_P) $(SHADOWDIR)/po
@@ -2777,6 +2777,8 @@
 	cp config.mk.dist $(SHADOWDIR)
 	$(MKDIR_P) $(SHADOWDIR)/xxd
 	cd $(SHADOWDIR)/xxd; ln -s ../../xxd/*.[ch] ../../xxd/Make* .
+	$(MKDIR_P) $(SHADOWDIR)/xdiff
+	cd $(SHADOWDIR)/xdiff; ln -s ../../xdiff/*.[ch] .
 	if test -d $(RSRC_DIR); then \
 		cd $(SHADOWDIR); \
 		ln -s ../infplist.xml .; \
diff --git a/src/version.c b/src/version.c
index f9e9cf4..3a2b065 100644
--- a/src/version.c
+++ b/src/version.c
@@ -795,6 +795,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    391,
+/**/
     390,
 /**/
     389,