syscall: add missing int flag argument to utimensat

Fixes #21437

Change-Id: I55fbf5114ae1bb7f4aa1a20450e8d5309756cd5b
Reviewed-on: https://go-review.googlesource.com/55430
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
diff --git a/src/syscall/syscall_darwin.go b/src/syscall/syscall_darwin.go
index 4d17b15..236ba3d 100644
--- a/src/syscall/syscall_darwin.go
+++ b/src/syscall/syscall_darwin.go
@@ -186,7 +186,7 @@
 	return
 }
 
-func utimensat(dirfd int, path string, times *[2]Timespec) error {
+func utimensat(dirfd int, path string, times *[2]Timespec, flag int) error {
 	// Darwin doesn't support SYS_UTIMENSAT
 	return ENOSYS
 }