https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91034
--- Comment #8 from Andrew Roberts <andrewm.roberts at sky dot com> --- Build of 9.1.0 using system gmp worked fine. Rebuild of 9.1.0 with in tree gmp-6.1.2 using that version of gcc also worked fine. Thus probably a host gcc compiler problem, I'll report to Raspbian.
