fix usage of system version of librocket
However, since someone could install that specialized version of libRocket separate I would be ok with this change if you add an option with which the usage of the system version could be enabled.
Since the "upstream" librocket seems pretty dead (their site that their repo points to has even been taken over), I kind of assumed your fork was the new "canonical" one. That's why I created https://aur.archlinux.org/packages/librocket-asarium-git/ (the patches from there are also in an open PR against your librocket repo, and opened a PR against the librocket/librocket repo too just in case they want to merge it).
@sandsmark Any chance of taking another look at this?