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.

src/version.c

@@ -799,6 +799,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    659,
 /**/
     658,
 /**/