Not that it matters much, but *both* of
-lm and -pthread are no-ops on Mac OS X
and should probably be removed from "dmd".

It's all in libSystem.B.dylib instead...
> lrwxr-xr-x  1 root  wheel  15 16 Mar  2004 /usr/lib/libm.dylib -> libSystem.dylib
> lrwxr-xr-x  1 root  wheel  15 16 Mar  2004 /usr/lib/libpthread.dylib -> libSystem.dylib

So libphobos.spec can pretty much be blank ?
> %rename lib liborig
> *lib: %(liborig)

--anders