Add top level build script for building packages.

ports/OpenSceneGraph/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
+BUILD_DIR=${NACL_PACKAGES_REPOSITORY}/${PACKAGE_NAME}
 
 ConfigureStep() {
-  Banner "Configuring ${PACKAGE_NAME}"
+  Banner "No configure step"
+}
+
+BuildStep() {
   # export the nacl tools
   export CC=${NACLCC}
   export CXX=${NACLCXX}
   export AR=${NACLAR}
   export RANLIB=${NACLRANLIB}
   export CFLAGS=${NACLPORTS_CFLAGS}
   export CXXFLAGS=${NACLPORTS_CXXFLAGS}
   export LDFLAGS=${NACLPORTS_LDFLAGS}
   export PATH=${NACL_BIN_PATH}:${PATH};
   export LIB_OSG=libosg.a
   export LIB_OSGUTIL=libosgUtil.a
   export LIB_OPENTHREADS=libOpenThreads.a
+  DefaultBuildStep
+}
 
-  ChangeDir ${NACL_PACKAGES_REPOSITORY}/${PACKAGE_NAME}
-}
 
 InstallStep() {
   Remove ${NACLPORTS_INCLUDE}/osg
   Remove ${NACLPORTS_INCLUDE}/osgUtil
   Remove ${NACLPORTS_INCLUDE}/OpenThreads
   readonly THIS_PACKAGE_PATH=${NACL_PACKAGES_REPOSITORY}/${PACKAGE_NAME}
   cp -R include/osg ${NACLPORTS_INCLUDE}/osg
   cp -R include/osgUtil ${NACLPORTS_INCLUDE}/osgUtil
   cp -R include/OpenThreads ${NACLPORTS_INCLUDE}/OpenThreads
   Remove ${NACLPORTS_LIBDIR}/libosg.a
   Remove ${NACLPORTS_LIBDIR}/libosgUtil.a
   Remove ${NACLPORTS_LIBDIR}/libOpenThreads.a
   install -m 644 ${LIB_OSG} ${NACLPORTS_LIBDIR}/${LIB_OSG}
   install -m 644 ${LIB_OSGUTIL} ${NACLPORTS_LIBDIR}/${LIB_OSGUTIL}
   install -m 644 ${LIB_OPENTHREADS} ${NACLPORTS_LIBDIR}/${LIB_OPENTHREADS}
 }
-
-
-PackageInstall
-exit 0