patch 8.2.2639: build failure when fsync() is not available

Problem:    Build failure when fsync() is not available.
Solution:   Add #ifdef.
diff --git a/src/version.c b/src/version.c
index 40411d8..e2519f4 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2639,
+/**/
     2638,
 /**/
     2637,