.travis.yml: Exclude only failing matrix entries
.travis.yml: Exclude only failing matrix entries

This improves over the previous commit (13d9083) since this way we can still test some compilation against clang.
BLLIP/bllip-parser,BLLIP/bllip-parser,BLLIP/bllip-parser,BLLIP/bllip-parser,BLLIP/bllip-parser,BLLIP/bllip-parser,BLLIP/bllip-parser,BLLIP/bllip-parser