Switch from using 'nacl_main' to 'main' entry point

ports/gimp/build.sh

 # Copyright (c) 2015 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.
 
 ConfigureStep() {
   EXTRA_CONFIGURE_ARGS+=" --disable-python --without-dbus --without-webkit"
   EXTRA_CONFIGURE_ARGS+=" --with-gnu-ld"
-  NACLPORTS_CPPFLAGS+=" -Dmain=nacl_main"
-  NACLPORTS_LDFLAGS+=" ${NACL_CLI_MAIN_LIB}"
-
+  EnableCliMain
   DefaultConfigureStep
 }
 
 PublishStep() {
   MakeDir ${PUBLISH_DIR}
   local APP_DIR="${PUBLISH_DIR}/${NACL_ARCH}"
   local TAR_ROOT="${APP_DIR}/root"
   MakeDir ${TAR_ROOT}
   MakeDir ${APP_DIR}
   ChangeDir ${APP_DIR}
@@ skipping 18 matching lines @@
    ./naclports-dummydir/etc
   LogExecute cp -rf ${INSTALL_DIR}/naclports-dummydir/share/*\
    ./naclports-dummydir/share
   LogExecute rm -Rf ./naclports-dummydir/share/man
 
   LogExecute tar -cvf gimp.tar *
   LogExecute cp gimp.tar ${APP_DIR}/gimp.tar
   shasum ${APP_DIR}/gimp.tar > ${APP_DIR}/gimp.tar.hash
   LogExecute rm -rf ${TAR_ROOT}
 }