build: make use of env

R=rsc, golang-dev
CC=golang-dev
https://golang.org/cl/5504053
diff --git a/src/buildscript_netbsd_amd64.sh b/src/buildscript_netbsd_amd64.sh
index 5a5637e..a85dac7 100755
--- a/src/buildscript_netbsd_amd64.sh
+++ b/src/buildscript_netbsd_amd64.sh
@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 # AUTO-GENERATED by buildscript.sh; DO NOT EDIT.
 # This script builds the go command (written in Go),
 # and then the go command can build the rest of the tree.