patch 8.1.1971: manually enabling features causes build errors

Problem:    Manually enabling features causes build errors. (John Marriott)
Solution:   Adjust #ifdefs.
diff --git a/src/version.c b/src/version.c
index 7b3fff0..85526b6 100644
--- a/src/version.c
+++ b/src/version.c
@@ -762,6 +762,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1971,
+/**/
     1970,
 /**/
     1969,