patch 8.0.0594: build failure when windows feature is missing

Problem:    Build failure when windows feature is missing.
Solution:   Add #ifdef.
diff --git a/src/version.c b/src/version.c
index 9e6eeac..6e2620d 100644
--- a/src/version.c
+++ b/src/version.c
@@ -765,6 +765,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    594,
+/**/
     593,
 /**/
     592,