Add gc build tag for the asm code.
Fixes #27.
diff --git a/decode_amd64.go b/decode_amd64.go
index 32bce47..cbcd464 100644
--- a/decode_amd64.go
+++ b/decode_amd64.go
@@ -2,6 +2,8 @@
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
+// +build gc
+
package snappy
// decode has the same semantics as in decode_other.go.
diff --git a/decode_amd64.s b/decode_amd64.s
index c33f5bf..099d096 100644
--- a/decode_amd64.s
+++ b/decode_amd64.s
@@ -2,6 +2,8 @@
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
+// +build gc
+
#include "textflag.h"
// func decode(dst, src []byte) int
diff --git a/decode_other.go b/decode_other.go
index 1a8114a..b557136 100644
--- a/decode_other.go
+++ b/decode_other.go
@@ -2,7 +2,7 @@
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
-// +build !amd64
+// +build !amd64 !gc
package snappy
