unix: support compiling with gccgo on linux/386

Implement socketcall and rawsocketcall in addition to seek (already
introduced in CL 100076) to support compiling with gccgo on linux/386

Change-Id: Iaa51aa159a4743ae0e394f541ff196e2d28aa27f
Reviewed-on: https://go-review.googlesource.com/117697
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

unix/syscall_linux_gccgo_arm.go

@@ -0,0 +1,20 @@
+// Copyright 2018 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.
+
+// +build linux,gccgo,arm
+
+package unix
+
+import (
+	"syscall"
+	"unsafe"
+)
+
+func seek(fd int, offset int64, whence int) (int64, syscall.Errno) {
+	var newoffset int64
+	offsetLow := uint32(offset & 0xffffffff)
+	offsetHigh := uint32((offset >> 32) & 0xffffffff)
+	_, _, err := Syscall6(SYS__LLSEEK, uintptr(fd), uintptr(offsetHigh), uintptr(offsetLow), uintptr(unsafe.Pointer(&newoffset)), uintptr(whence), 0)
+	return newoffset, err
+}