PHO authored Mar 14, 2013 and ian@well-typed.com committed Mar 17, 2013

On OpenBSD and NetBSD, we were accidentally passing "-optl-pthread" to
the gcc to build dynamic libraries because of a bitrotted hack for
those OSes, which resulted in a weird situation where every dynamic
library is named "ptl-pthread" and placed at "$(TOP)".

The hack in question were to work around a linkage problem with
libHSffi, but we no longer build it and just use libffi these days so
the hack can safely be removed.