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

ports/font-util/build.sh

 # 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.
 
 # The host build of this tool is needed by its dependents.
-HOST_BUILD_DIR=${WORK_DIR}/build-nacl-host
-HOST_INSTALL_DIR=${WORK_DIR}/install-nacl-host
+HOST_BUILD_DIR=${WORK_DIR}/build_host
+HOST_INSTALL_DIR=${WORK_DIR}/install_host
 
 EXECUTABLES="bdftruncate${NACL_EXEEXT} ucs2any${NACL_EXEEXT}"
 
 NACLPORTS_CPPFLAGS+=" -Dmain=nacl_main"
 NACLPORTS_LDFLAGS+=" -Dmain=nacl_main"
 export LIBS="-Wl,--undefined=nacl_main \
   ${NACL_CLI_MAIN_LIB} -lppapi_simple \
   -lnacl_io -lppapi -lppapi_cpp -l${NACL_CPP_LIB}"
 
 if [ "${NACL_LIBC}" = "newlib" ]; then
@@ skipping 13 matching lines @@
 ConfigureStep() {
   BuildForHost
   ChangeDir ${BUILD_DIR}
   DefaultConfigureStep
 }
 
 InstallStep() {
   DefaultInstallStep
   PublishByArchForDevEnv
 }