Draft: Attempt to solve FTBFS on armel

See https://bugzilla.mozilla.org/show_bug.cgi?id=1786619 and https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1017961. Current status is that it builds, but there are enough segfaults during unit testing that I am not confident that the resulting binaries wouldn't deserve grave bugs if we ignored the test failures.

/cc @bunk