Fix issue 3402 . The initial suggestion of using readlink doesn't

utils/compiler/build_helper.dart

 // 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.
 
 #import('dart:io');
 #import('dart:uri');
 
 #import('../../lib/compiler/implementation/util/uri_extras.dart');
 #import('../../lib/compiler/implementation/filenames.dart');
 
@@ skipping 80 matching lines @@
   print('${name}PathWin = $pathWin');
 
   // Tell the VM to grow the heap more aggressively. This should only
   // be necessary temporarily until the VM is better at detecting how
   // applications use memory.
   // TODO(ahe): Remove this option.
   options = ' --heap_growth_rate=32$options';
 
   return [
 '''
-#!/bin/sh
+#!/bin/bash
 # 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.
 
-BIN_DIR=`dirname \$0`
+# 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)"
+
 unset COLORS
 if test -t 1; then
   # Stdout is a terminal.
   if test 8 -le `tput colors`; then
     # Stdout has at least 8 colors, so enable colors.
     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
 REM Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 REM for details. All rights reserved. Use of this source code is governed by a
 REM BSD-style license that can be found in the LICENSE file.
 
 set SCRIPTPATH=%~dp0
 
 REM Does the path have a trailing slash? If so, remove it.
 if %SCRIPTPATH:~-1%==\ set SCRIPTPATH=%SCRIPTPATH:~0,-1%
 
 set arguments=%*
 
 "%SCRIPTPATH%\dart.exe"$options "%SCRIPTPATH%$pathWin" %arguments%
 '''.replaceAll('\n', '\r\n')];
 }