The old code was trying to pass -Wgnu-zero-variadic-macro-arguments
as part of CXXFLAGS, but it forgot the quotation marks needed around
whitespace. This meant that option was ignored:
https://travis-ci.org/github/google/googletest/jobs/666534177#L760

Unfortunately, the codebase is not remotely clean with respect to that
warning option. It fails like this:
https://travis-ci.org/github/Quuxplusone/googletest/jobs/668118135

So, remove that failing configuration from the test matrix until
someone has time to look at it.