Build gtest from source rather than using SDK-provided version

ports/libyuv/build.sh

 # Copyright 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="convert libyuv_unittest"
 
 # Workaround for arm-gcc bug:
 # https://code.google.com/p/nativeclient/issues/detail?id=3205
 # TODO(sbc): remove this once the issue is fixed
 if [ "${NACL_ARCH}" = "arm" ]; then
   NACLPORTS_CPPFLAGS+=" -mfpu=vfp"
 fi
 
 EnableGlibcCompat
 
 if [ "${NACL_ARCH}" = "x86_64" ]; then
   NACLPORTS_CPPFLAGS+=" -DLIBYUV_DISABLE_X86=1"
 fi
 
 EXTRA_CMAKE_ARGS="-DTEST=ON"
+EXTRA_CMAKE_ARGS+=" -DGTEST_SRC_DIR=${GTEST_SRC}"
 
 TestStep() {
   # TODO(sbc): re-enable i686 testing once we fix this gtest-releated issue:
   # http://crbug.com/434821
   if [ "${NACL_ARCH}" = "i686" ]; then
     return
   fi
   if [ "${NACL_ARCH}" = pnacl ]; then
     return
   fi
   LogExecute ./libyuv_unittest.sh --gtest_filter=-libyuvTest.ARGBRect_Unaligned
 }