misc/cgo/test/issue9400: fix to build with gccgo

This doesn't test much with gccgo, but at least it builds now, and the
test does, unsurprisingly, pass.  A proper test would require adding
assembly files in GCC syntax for all platforms that gccgo supports,
which would be infeasible.

Also added copyright headers to the asm files.

Change-Id: Icea5af29d7d521a0681506ddb617a79705b76d33
Reviewed-on: https://go-review.googlesource.com/9417Reviewed-by: Minux Ma <minux@golang.org>

misc/cgo/test/issue9400/asm_386.s

+// 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.
+
+// +build !gccgo
+
 #include "textflag.h"
 
 TEXT ·RewindAndSetgid(SB),NOSPLIT,$0-0

misc/cgo/test/issue9400/asm_amd64x.s

+// 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.
+
 // +build amd64 amd64p32
+// +build !gccgo
 
 #include "textflag.h"
 

misc/cgo/test/issue9400/asm_arm.s

+// 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.
+
+// +build !gccgo
+
 #include "textflag.h"
 
 TEXT cas<>(SB),NOSPLIT,$0

misc/cgo/test/issue9400/asm_arm64.s

+// 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.
+
+// +build !gccgo
+
 #include "textflag.h"
 
 TEXT ·RewindAndSetgid(SB),NOSPLIT,$-8-0

misc/cgo/test/issue9400/asm_ppc64x.s

+// 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.
+
 // +build ppc64 ppc64le
+// +build !gccgo
 
 #include "textflag.h"
 

misc/cgo/test/issue9400/gccgo.go

+// 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.
+
+// +build gccgo
+
+package issue9400
+
+import (
+	"runtime"
+	"sync/atomic"
+)
+
+// The test for the gc compiler resets the stack pointer so that the
+// stack gets modified.  We don't have a way to do that for gccgo
+// without writing more assembly code, which we haven't bothered to
+// do.  So this is not much of a test.
+
+func RewindAndSetgid() {
+	atomic.StoreInt32(&Baton, 1)
+	for atomic.LoadInt32(&Baton) != 0 {
+		runtime.Gosched()
+	}
+}