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)
diff --git a/src/evalfunc.c b/src/evalfunc.c
index 6538b36..e693ef9 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -14791,7 +14791,7 @@
 	else if (do_fsync)
 	    // Ignore the error, the user wouldn't know what to do about it.
 	    // May happen for a device.
-	    vim_ignored = fsync(fileno(fd));
+	    vim_ignored = vim_fsync(fileno(fd));
 #endif
 	fclose(fd);
     }
@@ -14803,7 +14803,7 @@
 	else if (do_fsync)
 	    /* Ignore the error, the user wouldn't know what to do about it.
 	     * May happen for a device. */
-	    vim_ignored = fsync(fileno(fd));
+	    vim_ignored = vim_fsync(fileno(fd));
 #endif
 	fclose(fd);
     }