Add top level build script for building packages.

ports/drod/build.sh

 #!/bin/bash
 # Copyright (c) 2013 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
-
 PACKAGE_DIR=drod-213fa477000429fb9a5f4a77673394d47cadbfac
-source ../../build_tools/common.sh
-
+EXECUTABLES=custom/bin/drod
+BUILD_DIR=${NACL_PACKAGES_REPOSITORY}/${PACKAGE_DIR}/Caravel/Master/Linux
+MAKE_TARGETS="drod-custom"
 export DESTDIR=${PUBLISH_DIR}/.data
-EXECUTABLES=custom/bin/drod
 
 ConfigureStep() {
   export CC=${NACLCC}
   export CXX=${NACLCXX}
   export AR="${NACLAR} cr"
   export RANLIB=${NACLRANLIB}
   export CXXFLAGS="${NACLPORTS_CXXFLAGS} -Wno-write-strings"
   export SDL_CONFIG=${NACLPORTS_PREFIX}/bin/sdl-config
   export LDFLAGS_common=${NACLPORTS_LDFLAGS}
   export EXTRA_LIBS="-lSDL_mixer -lSDL -lmikmod -lvorbisfile -lvorbisenc \
                      -lvorbis -logg -lfreetype -lSDLmain -ltar -lnacl_io"
 }
 
-BuildStep() {
-  ChangeDir ${NACL_PACKAGES_REPOSITORY}/${PACKAGE_DIR}/Caravel/Master/Linux
-  export MAKE_TARGETS="drod-custom"
-  DefaultBuildStep
-}
-
 InstallStep() {
   DefaultInstallStep
 
   ChangeDir ${DESTDIR}
   mv usr/local/games/drod ${PUBLISH_DIR}/drod_${NACL_ARCH}${NACL_EXEEXT}
   tar cf ${PUBLISH_DIR}/drod_usr.tar usr
   tar cf ${PUBLISH_DIR}/drod_var.tar var
   rm -rf ${DESTDIR}
   cp ${START_DIR}/drod.html ${PUBLISH_DIR}
   ChangeDir ${PUBLISH_DIR}
   python ${NACL_SDK_ROOT}/tools/create_nmf.py \
       drod_*${NACL_EXEEXT} \
       -s . \
       -o drod.nmf
   if [ ${NACL_ARCH} = pnacl ]; then
     sed -i.bak 's/x-nacl/x-pnacl/g' ${PUBLISH_DIR}/drod.html
   fi
 }
-
-PackageInstall
-exit 0