tools: use /usr/bin/env for bash/sh invocation

This implements GitHub PR #115 on the current repo state. /usr/bin/env
is already used for other (cmake/python/etc) invocations, and this PR
brings bash/sh into line with that for slightly improved portability.

Co-authored-by: Douglas Wilson <douglas.wilson@gmail.com>
Signed-off-by: Gerwin Klein <gerwin.klein@proofcraft.systems>

tools/cpp_gen.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 #
 # Copyright 2020, Data61, CSIRO (ABN 41 687 119 230)
 #

tools/dts/update-dts.sh

@@ -1,4 +1,4 @@
-#!/bin/sh
+#!/usr/bin/env sh
 #
 # Copyright 2020, Data61, CSIRO (ABN 41 687 119 230)
 #

tools/kernel_pylint.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 #
 # Copyright 2020, Data61, CSIRO (ABN 41 687 119 230)
 #

tools/kernel_xmllint.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 #
 # Copyright 2020, Data61, CSIRO (ABN 41 687 119 230)
 #

tools/xmllint.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 #
 # Copyright 2020, Data61, CSIRO (ABN 41 687 119 230)
 #