patch 8.2.4039: the xdiff library is linked in even when not used
Problem: The xdiff library is linked in even when not used.
Solution: Use configure to decide whether xdiff object files are included.
diff --git a/src/feature.h b/src/feature.h
index fcd0d4b..b2df6f9 100644
--- a/src/feature.h
+++ b/src/feature.h
@@ -345,8 +345,9 @@
/*
* +diff Displaying diffs in a nice way.
* Requires +windows and +autocmd.
+ * Can be enabled in autoconf already.
*/
-#if defined(FEAT_NORMAL)
+#if defined(FEAT_NORMAL) && !defined(FEAT_DIFF)
# define FEAT_DIFF
#endif