What version of git (git --version) do you have? The -c option is ancient… I don’t recall what version it was added but way way back in the v1 era as I recall. You do have at least version 2.x of git installed to start with (even v2 is many many years old, like 6 or 7 years old I think)?
EDIT: If you do have a git version older than v2 then you really badly need to update it. V1 had insecure hash generation (not just theoretically) that has since been updated along with a lot of other security fixes, not to mention all the other security and other fixes since v2.0.0 first came out.
