patch 8.1.0915: fsync() may not work properly on Mac

Problem:    fsync() may not work properly on Mac.
Solution:   Use fcntl() with F_FULLFSYNC. (suggested by Justin M. Keyes)

src/version.c

@@ -783,6 +783,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    915,
 /**/
     914,
 /**/