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

@@ -4,6 +4,7 @@
 
 // +build !appengine
 // +build gc
+// +build go1.6
 // +build !noasm
 
 package vector

vector/acc_amd64.s

@@ -2,6 +2,7 @@
 
 // +build !appengine
 // +build gc
+// +build go1.6
 // +build !noasm
 
 #include "textflag.h"

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
 

vector/gen_acc_amd64.s.tmpl

@@ -4,6 +4,7 @@
 
 // +build !appengine
 // +build gc
+// +build go1.6
 // +build !noasm
 
 #include "textflag.h"