patch 8.1.1687: the evalfunc.c file is too big

Problem:    The evalfunc.c file is too big.
Solution:   Move testing support to a separate file.

src/version.c

@@ -777,6 +777,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1687,
 /**/
     1686,
 /**/