Boost typedef warnings break compilation with GCC 4.8.2 on OS X Mavericks

After upgrading to OS X 10.9, I had to reinstall GCC since it was replaced with clang by Apple. I installed GCC 4.8.2 with Homebrew, created a new build directory, configured it with `CC=gcc-4.8 CXX=g++-4.8 ../configure`, and then ran `make`.

Boost has dozens of warnings, all with the same message. Since all warnings are treated as errors, they break the build. This is a small sample:

../3rdparty/libprocess/3rdparty/boost-1.53.0/boost/variant/variant.hpp: In member function 'void boost::variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, T18, T19>::operator<(const U&) const':
../3rdparty/libprocess/3rdparty/boost-1.53.0/boost/static_assert.hpp:125:21: error: typedef 'boost_static_assert_typedef_2254' locally defined but not used [-Werror=unused-local-typedefs]
BOOST_JOIN(boost_static_assert_typedef_, _LINE_)
^
../3rdparty/libprocess/3rdparty/boost-1.53.0/boost/variant/variant.hpp:2254:9: note: in expansion of macro 'BOOST_STATIC_ASSERT'
BOOST_STATIC_ASSERT( false && sizeof(U) );
^