patch 7.4.1976
Problem:    Number variables are not 64 bits while they could be.
Solution:   Add the num64 feature. (Ken Takata)
diff --git a/src/fold.c b/src/fold.c
index e4c7f41..35ceceb 100644
--- a/src/fold.c
+++ b/src/fold.c
@@ -3032,7 +3032,7 @@
     /* KeyTyped may be reset to 0 when calling a function which invokes
      * do_cmdline().  To make 'foldopen' work correctly restore KeyTyped. */
     save_keytyped = KeyTyped;
-    n = eval_foldexpr(flp->wp->w_p_fde, &c);
+    n = (int)eval_foldexpr(flp->wp->w_p_fde, &c);
     KeyTyped = save_keytyped;
 
     switch (c)