exp/ssa/interp: fix build for Plan 9

R=adonovan, minux.ma, alex.brainman, akumar, rminnich
CC=golang-dev, lucio.dere
https://golang.org/cl/7300078

src/pkg/exp/ssa/interp/external_plan9.go

+// Copyright 2013 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 interp
+
+import (
+	"exp/ssa"
+	"syscall"
+)
+
+func ext۰syscall۰Kill(fn *ssa.Function, args []value) value {
+	panic("syscall.Kill not yet implemented")
+}
+
+func ext۰syscall۰Write(fn *ssa.Function, args []value) value {
+	// We could emulate syscall.Syscall but it's more effort.
+	p := args[1].([]value)
+	b := make([]byte, 0, len(p))
+	for i := range p {
+		b = append(b, p[i].(byte))
+	}
+	n, _ := syscall.Write(args[0].(int), b)
+	err := iface{} // TODO(adonovan): fix: adapt concrete err to interpreted iface.
+	return tuple{n, err}
+}

src/pkg/exp/ssa/interp/external_unix.go

@@ -28,5 +28,4 @@ func ext۰syscall۰Write(fn *ssa.Function, args []value) value {
 	n, _ := syscall.Write(args[0].(int), b)
 	err := iface{} // TODO(adonovan): fix: adapt concrete err to interpreted iface.
 	return tuple{n, err}
-
 }