Add top level build script for building packages.

ports/jsoncpp/build.sh

 #!/bin/bash
 # Copyright (c) 2012 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
 
 
 BuildStep() {
   Banner "Building ${PACKAGE_NAME}"
   export PACKAGE_DIR="${NACL_PACKAGES_REPOSITORY}/${PACKAGE_NAME}"
   ChangeDir ${PACKAGE_DIR}
 
   export CXXCMD="${NACLCC} -Iinclude -I."
   LogExecute ${CXXCMD} -c src/lib_json/json_reader.cpp
   LogExecute ${CXXCMD} -c src/lib_json/json_value.cpp
   LogExecute ${CXXCMD} -c src/lib_json/json_writer.cpp
 
   LogExecute ${NACLAR} rcs libjsoncpp.a \
     json_reader.o \
     json_value.o \
     json_writer.o
 
   LogExecute ${NACLRANLIB} libjsoncpp.a
 }
 
 
 InstallStep() {
   Banner "Installing ${PACKAGE_NAME}"
   export PACKAGE_DIR="${NACL_PACKAGES_REPOSITORY}/${PACKAGE_NAME}"
 
   LogExecute cp ${PACKAGE_DIR}/libjsoncpp.a ${NACLPORTS_LIBDIR}
   LogExecute cp -R ${PACKAGE_DIR}/include/json ${NACLPORTS_INCLUDE}
 }
-
-
-PackageInstall
-exit 0