Reduce the number of times we build a host copy of python.

ports/python-static/build.sh

 # Copyright (c) 2014 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.
 
 EXECUTABLES=python${NACL_EXEEXT}
 
 # Currently this package only builds on linux.
 # The build relies on certain host binaries and python's configure
 # requires us to set --build= as well as --host=.
 #
 # The module downloader is patterned after the Bochs image downloading step.
 
 ConfigureStep() {
   SetupCrossEnvironment
   export CROSS_COMPILE=true
   # We pre-seed configure with certain results that it cannot determine
   # since we are doing a cross compile.  The $CONFIG_SITE file is sourced
   # by configure early on.
   export CONFIG_SITE=${START_DIR}/config.site
   # Disable ipv6 since configure claims it requires a working getaddrinfo
   # which we do not provide.  TODO(sbc): remove this once nacl_io supports
   # getaddrinfo.
   EXTRA_CONFIGURE_ARGS="--disable-ipv6"
   EXTRA_CONFIGURE_ARGS+=" --with-suffix=${NACL_EXEEXT}"
   EXTRA_CONFIGURE_ARGS+=" --build=i686-linux-gnu --disable-shared --enable-static"
   export SO=.a
-  export MAKEFLAGS="PGEN=${NACL_HOST_PYROOT}/../python-host/build-nacl-host/Parser/pgen"
+  export MAKEFLAGS="PGEN=${NACL_HOST_PYBUILD}/Parser/pgen"
   export LIBS="-ltermcap"
   export DYNLOADFILE=dynload_ppapi.o
   export MACHDEP=ppapi
   export LINKCC=${NACLCXX}
   if [ "${NACL_LIBC}" = "newlib" ]; then
     LIBS+=" -lglibc-compat -lc"
   fi
   LogExecute cp ${START_DIR}/dynload_ppapi.c ${SRC_DIR}/Python/
   # This next step is costly, but it sets the environment variables correctly.
   DefaultConfigureStep
@@ skipping 18 matching lines @@
     PY_LINK_LINE+=" -lglibc-compat"
   fi
   echo ${PY_LINK_LINE} >> Modules/Setup.local
   # At this point we use the existing environment variables from
   # DefaultConfigureStep to build our destination Python modules
 }
 
 BuildStep() {
   SetupCrossEnvironment
   export CROSS_COMPILE=true
-  export MAKEFLAGS="PGEN=${NACL_HOST_PYROOT}/../python-host/build-nacl-host/Parser/pgen"
+  export MAKEFLAGS="PGEN=${NACL_HOST_PYBUILD}/Parser/pgen"
   DefaultBuildStep
   ChangeDir ${BUILD_DIR}
   Banner "Rebuilding libpython2.7.a"
   ${AR} cr libpython2.7.a ${DEST_PYTHON_OBJS}/*/*.o
   ${RANLIB} libpython2.7.a
   # To avoid rebuilding python.nexe with the new libpython2.7.a and duplicating
   # symbols
   LogExecute touch python${NACL_EXEEXT}
   # The modules get built with SO=so, but they need to be SO=a inside the
   # destination filesystem.
   for fn in $(find ${NACL_DEST_PYROOT}/${SITE_PACKAGES} -name "*.so"); do
     LogExecute touch ${fn%%so}a
     LogExecute rm -v ${fn}
   done
 }