angr-vex's library is dlopen(3)ed py py-pyvex (not py-angr itself), so
register it as proper RDEP in py-pyvex (and only there).
Spotted after `pkg_add angrop' on a fresh installation where angr-vex was
not installed; even though angr has an LDEP on it, our framework does not
turn it into a RDEP unless angr also links against it.
c75d2640cb