vector: add go1.6 build tag for asm code.

Go 1.5 doesn't understand amd64 opcode mnemonics like PADDD or PMULLD.

Change-Id: Ic31ab4d2a8a222ca18288387de40db6ce673d7f1
Reviewed-on: https://go-review.googlesource.com/32132
Reviewed-by: David Crawshaw <crawshaw@golang.org>

 vector/acc_amd64.go         | 1 +
 vector/acc_amd64.s          | 1 +
 vector/acc_other.go         | 2 +-
 vector/gen_acc_amd64.s.tmpl | 1 +
 4 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/vector/acc_amd64.go b/vector/acc_amd64.go
index cf535fc..68f6e03 100644
--- a/vector/acc_amd64.go
+++ b/vector/acc_amd64.go
@@ -4,6 +4,7 @@
 
 // +build !appengine
 // +build gc
+// +build go1.6
 // +build !noasm
 
 package vector
diff --git a/vector/acc_amd64.s b/vector/acc_amd64.s
index dee7ad1..299e052 100644
--- a/vector/acc_amd64.s
+++ b/vector/acc_amd64.s
@@ -2,6 +2,7 @@
 
 // +build !appengine
 // +build gc
+// +build go1.6
 // +build !noasm
 
 #include "textflag.h"
diff --git a/vector/acc_other.go b/vector/acc_other.go
index c98d20b..30425be 100644
--- a/vector/acc_other.go
+++ b/vector/acc_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 appengine !gc noasm
+// +build !amd64 appengine !gc !go1.6 noasm
 
 package vector
 
diff --git a/vector/gen_acc_amd64.s.tmpl b/vector/gen_acc_amd64.s.tmpl
index 05ce25b..66b21a1 100644
--- a/vector/gen_acc_amd64.s.tmpl
+++ b/vector/gen_acc_amd64.s.tmpl
@@ -4,6 +4,7 @@
 
 // +build !appengine
 // +build gc
+// +build go1.6
 // +build !noasm
 
 #include "textflag.h"