CMake has the ability to build itself it's own self-contained internal
libraries, including libarchive, which tend to be very compatible
We might someday have an option to make it do this for situations such
as this maybe, but for now, you can try to do it manually.
in the depends_lib-append section of the portfile, delete the line
with the port:libarchive requirement.
you can override just libarchive (look here
<https://github.com/Kitware/CMake/blob/master/CMakeLists.txt> for the
magic variables to use) or you can try just going down to the platform
darwin 8 block (which is set up like this for Tiger) and try putting
your version of darwin in there, whatever it is, to delete the
--system-libs requirement and force cmake to build using it's internal
You might need to monkey around a bit more to get it to work.
if you really mess up and want to start over, do a "sudo port sync"
and the portfiles will be put back to original status