I was expecting this to fail to compile somewhere, maybe in the CI, but that doesn't seem to be the case?
Seems workable given the SSP related changes in the newer mingw-w64 headers (which are in Guix):

    Implement some of the stack protector functions/variables so -lssp is now optional when _FORTIFY_SOURCE or -fstack-protector-strong is used.

However I think this would still be broken in some older environments, so we might have to wait for a compiler bump, or similar. The optional -lssp also seems to work when using older headers, which doesn't make sense.