Wow, thanks for doing all that work.To simplify this sort of thing in the future, I suggest that Gnulib drop support for IRIX, as IRIX has no user community outside of computer museums and SGI has not supported it since 2013. (Had we dropped IRIX support already, your email would have been half as long. :-)
GNU Emacs essentially dropped support for IRIX in Emacs 25.1 (2016) and nobody has seemed to notice or care.
