unix: add FcntlInt

Fixes golang/go#24649
Fixes golang/go#24677

Change-Id: I3faa74ab68e093a097c3f2a8ec7c054431bdfb3f
Reviewed-on: https://go-review.googlesource.com/104736
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

unix/fcntl_linux_32bit.go

@@ -0,0 +1,13 @@
+// +build linux,386 linux,arm linux,mips linux,mipsle
+
+// Copyright 2014 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package unix
+
+func init() {
+	// On 32-bit Linux systems, the fcntl syscall that matches Go's
+	// Flock_t type is SYS_FCNTL64, not SYS_FCNTL.
+	fcntl64Syscall = SYS_FCNTL64
+}