available on your system (from Apple) but are required in newer versions
built by Homebrew: autoconf, automake, libtool, libffi (maybe others).
Without linking "libffi" for example, the check for pygobject3 will fail.
+ - We currently hardcode the build to use Qt 5.5 (not the latest available
+ version) in order to remain compatible with some older Mac OS X versions.
Building