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

ports/busybox/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="busybox"
 
-NACLPORTS_LDFLAGS+=" ${NACL_CLI_MAIN_LIB}"
-NACLPORTS_CPPFLAGS+=" -Dmain=nacl_main"
+EnableCliMain
 
 ConfigureStep() {
   cp "${START_DIR}/defconfig" .
 
   if [ "${TOOLCHAIN}" = "glibc" -a "${NACL_ARCH}" = "arm" ]; then
    echo "CONFIG_INIT=n" >> defconfig
    echo "CONFIG_LINEEDIT=n" >> defconfig
    echo "CONFIG_FEATURE_UTMP=n" >> defconfig
    echo "CONFIG_FEATURE_VI_USE_SIGNALS=n" >> defconfig
   fi
@@ skipping 36 matching lines @@
   if [[ ${TOOLCHAIN} = pnacl ]]; then
     return
   fi
 
   # Simple test of "cat" command to ensure basic functionality
   # TODO(sbc): run the full test suite
   echo "Running ./busybox.sh cat busybox.sh > test.out"
   $(./busybox.sh cat busybox.sh > test.out)
   LogExecute diff -u busybox.sh test.out
 }