* Add BENCHMARK_BUILD_32_BITS option and add builders to test it
* Attempt to fix travis configuration
* Make add_required_cxx_compiler_flag cause an error when the flag isn't supported
* add gcc-multilib dependancy on travis
* attempt to fix travis.yml parsing error
* Require g++-multilib instead of gcc-multilib
* Add 32 bit release configurations
* Attempt to fix libc++ travis build w/ 32 bits
* Work around CMake configuration failure on Travis
