revert change 13025.

utils/compiler/build_helper.dart

Index: utils/compiler/build_helper.dart
===================================================================
--- utils/compiler/build_helper.dart	(revision 13026)
+++ utils/compiler/build_helper.dart	(working copy)
@@ -98,19 +98,12 @@
 
   return [
 '''
-#!/bin/bash
+#!/bin/sh
 # Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
-# The following line MUST be the first command in the script.
-ABS_SCRIPT_PATH="\$_"
-
-# Setting BIN_DIR this way is ugly, but is needed to handle the case where
-# dart-sdk/bin has been symlinked to. On MacOS, readlink doesn't work
-# with this case.
-BIN_DIR="\$(cd "\${ABS_SCRIPT_PATH%/*}" ; pwd -P)"
-
+BIN_DIR=`dirname \$0`
 unset COLORS
 if test -t 1; then
   # Stdout is a terminal.
@@ -119,7 +112,7 @@
     COLORS="--enable-diagnostic-colors"
   fi
 fi
-exec "\$BIN_DIR"/dart$options "\$BIN_DIR/$path" \$COLORS "\$@"
+exec \$BIN_DIR/dart$options \$BIN_DIR/$path \$COLORS "\$@"
 ''',
 '''
 @echo off