travis: enable clang builds now that the LLVM repos are back up
travis: enable clang builds now that the LLVM repos are back up

nicksay/brotli,szabadka/brotli,anthrotype/brotli,anthrotype/brotli,google/brotli,nicksay/brotli,nicksay/brotli,nicksay/brotli,nicksay/brotli,szabadka/brotli,szabadka/brotli,anthrotype/brotli,szabadka/brotli,google/brotli,anthrotype/brotli,google/brotli,google/brotli,nicksay/brotli,google/brotli,google/brotli,nicksay/brotli,google/brotli,anthrotype/brotli,google/brotli