Make M-x shell work in emacs.

ports/gcc/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.
 
 export EXTRA_LIBS="${NACL_CLI_MAIN_LIB}"
+NACLPORTS_CPPFLAGS+=" -Dpipe=nacl_spawn_pipe"
 
 # --with-build-sysroot is necessary to run "fixincl"
 # properly. Without this option, GCC's build system tries to create
 # "include-fixed" based on the host's include directory, which is
 # not compatible with nacl-gcc.
 EXTRA_CONFIGURE_ARGS="\
     --enable-languages=c,c++ --disable-nls \
     --target=x86_64-nacl \
     --disable-libstdcxx-pch --enable-threads=nacl"
 
 # Force gcc to think that makeinfo is old so it won't build documentation.
 # Actually the issue is that its too new on most installs these days
 # (Ubunut/Trusty for example) and causes the build to break.
 export gcc_cv_prog_makeinfo_modern=no
 
 ConfigureStep() {
   DefaultConfigureStep
   for cache_file in $(find . -name config.cache); do
     Remove $cache_file
   done
 }