so... I found this. https://gcc.gnu.org/git/ (or maybe rather git:// gcc.gnu.org/gcc.git ) which I have cloned, but when I build this version, there's a checksum difference in stage 2 and 3 libiberty (and a few other objects). What might be a good, recent, version to build from? I also had to make some minor changes to force 'HAVE_PSIGNAL' in libiberty config.in and opt-suggestions.c failed with selftest.c which generates an assert about option "-" (commented out assert) And maybe it's either of those changes causes the issue because there is some option in the scripts that is deliberately bad and should generate a suggestion? (I doubt it).
