Add top level build script for building packages.

ports/jpeg6b/build.sh

 #!/bin/bash
 # Copyright (c) 2011 The Native Client Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-source pkg_info
-source ../../build_tools/common.sh
 
 EXECUTABLES="cjpeg djpeg jpegtran rdjpgcom wrjpgcom"
 
 InstallStep() {
   MakeDir ${NACLPORTS_PREFIX}/man
 }
 
 TestStep() {
   for exe in ${EXECUTABLES}; do
     mv ${exe} ${exe}${NACL_EXEEXT}
   done
 
   if [ ${NACL_ARCH} = "pnacl" ]; then
     for arch in x86-32 x86-64; do
       for exe in ${EXECUTABLES}; do
         WriteSelLdrScriptForPNaCl ${exe} ${exe}.${arch}.nexe ${arch}
       done
       make test
     done
   else
     for exe in ${EXECUTABLES}; do
       WriteSelLdrScript ${exe} ${exe}${NACL_EXEEXT}
     done
     make test
   fi
 }
-
-DefaultPackageInstall
-exit 0