Remove readIface's unused argument
Remove a bitrotted hack for OpenBSD and NetBSD regarding the dyn way.

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.
Enable Opt_PIC for the dyn way regardless of OSes.

We were previously enabling Opt_PIC on certain OSes namely Windows,
Darwin and Linux, but it should always be enabled for the dyn way
because it makes no sense to try to generate non-PIC dynamic
libraries, which is usually impossible.