Build gtest from source rather than using SDK-provided version

ports/nacl-spawn/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.
 
 NACLPORTS_CPPFLAGS+=" -I${START_DIR}"
 
 if [[ ${TOOLCHAIN} != emscripten ]]; then
   EXECUTABLES="test/unittests"
 fi
 
@@ skipping 22 matching lines @@
   cp -rf ${START_DIR}/* ${BUILD_DIR}
 }
 
 BuildStep() {
   if [[ ${TOOLCHAIN} == emscripten ]]; then
     return
   fi
   SetupCrossEnvironment
   export TOOLCHAIN
   export NACL_SHARED
+  export GTEST_DIR=${NACL_PREFIX}/src/gtest
   DefaultBuildStep
 }
 
 TestStep() {
   if [[ ${TOOLCHAIN} == emscripten ]]; then
     return
   fi
   if [[ ${NACL_LIBC} == glibc ]]; then
     SetupCrossEnvironment
     export TOOLCHAIN
@@ skipping 14 matching lines @@
   MakeDir ${DESTDIR_LIB}
   LogExecute cp libnacl_spawn.a ${DESTDIR_LIB}
   if [[ ${NACL_SHARED} == 1 ]]; then
     LogExecute cp libnacl_spawn.so ${DESTDIR_LIB}
   fi
   LogExecute cp libcli_main.a ${DESTDIR_LIB}
   MakeDir ${DESTDIR_INCLUDE}
   LogExecute cp -f ${START_DIR}/include/spawn.h ${DESTDIR_INCLUDE}/
   LogExecute cp -f ${START_DIR}/include/nacl_main.h ${DESTDIR_INCLUDE}/
 }