patch 8.1.0659: build failure without the sign feature

Problem:    Build failure without the sign feature.
Solution:   Put the sign struct declarations outside of the #ifdef.
diff --git a/src/version.c b/src/version.c
index 1772cfd..e76bf4b 100644
--- a/src/version.c
+++ b/src/version.c
@@ -800,6 +800,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    659,
+/**/
     658,
 /**/
     657,