[R-pkg-team] Bug#980809: rmatrix: breaks autopkgtest of r-cran-glmmtmb on s390x

[Graham Inggs]

Control: forwarded -1 https://github.com/glmmTMB/glmmTMB/issues/665

After another detour via #981623, r-cran-glmmtmb is now also rebuilt.
Even with the rebuilt r-cran-glmmtmb, I still see the "gradient
function must return a numeric vector of length" errors on s390x and
ppc64, which are both big-endian architectures.