Can't build with Visual Studio 15.5

Our dependency GoogleTest builds with -Werror, which normally is fine, except when updated developer tools start throwing more warnings. From the VS team:

In VS 2017's second toolset update, I'm going to deprecate the std::tr1 namespace (with the deprecated attribute, emitting compiler warnings) in both the C+14 and C+17 modes. This will cause googletest's use of std::tr1 to emit warnings (breaking builds under /WX).

While I will provide an escape-hatch macro to silence the deprecation warnings, googletest should migrate away from using std::tr1, as it will be removed in the future (eventually completely, with no escape hatches).

We will need to deal with this in Mesos itself eventually, but shouldn't disable Mesos' warning. However, we need to disable Googletest's warning until their patch is released in an update (and we consume or patch in that update).