I'm having some difficulty building OpenImageIO on macos (Snow
Leopard), as a required pre-requisite for building OSL. The build of
the external packages fails because libtiff doesn't build. Everything
else does.

I simply did a clean pull from the repository and followed the
instructions (and I've built dozens of open source things before, so
the issue is not unfamiliarity with make systems or anything like
that).

I've done all the usual sorts of troubleshooting, but nothing strikes
me as obviously wrong with the set up. Before I dig in seriously to
work out why the build is failing, I thought I would potentially save
some time by asking here first if anyone has successfully built on
macos after a fresh pull of OIIO and OSL, and if not, what issues and
resolutions might have got things working.

Thanks