A set of fixes which allow compilation of a basic Cactus configuration using Apple's clang compiler on Mac OS without Fortran. Note: probably not ready to be merged in current state; please comment!
These changes look fine apart from the minor issues described below.
Is there a trac ticket? If not, please open one.
I worked on this just before several conflicting commits were made, especially regarding the static_assert issue, and I think Roland said I should be very careful not to undo what was done in those. I don't have time to look into the issues right now. It would be nice to have, but someone should look through each commit and make sure it makes sense. Most of the conflicts below are from the auto-generated configure script. I probably should not have included that in the pull request. I just created a ticket: https://trac.einsteintoolkit.org/ticket/1933.
Most of these have since been implemented in Cactus or made obsolete.