Thiago tried building with a cherry-picked 70e484e885637c495be5481983dae2207fdd67bb and reports that:
For some reason I didn't understand, the problem I first reported
about rktboot/main.rkt failing during the build of
chez-scheme-for-racket-bootstrap-bootfiles came back. I had to increase
STACK_SAFETY_MARGIN again. I simply increased it 10x to make sure it
would work. If you want I can experiment with different values to find
an appropriate one.
So, as you suggested in:
it seems like there's still some underlying problem. I don't think I know enough about BC internals to have any useful ideas.
For now, unless you have a better idea, I'll propose using the 10x larger STACK_SAFETY_MARGIN for Guix and hope that works well enough to bootstrap CS. Whatever the problem with BC on ppc64le is, I expect it would also be triggered by other Racket programs, so Guix using CS by default on all platforms still seems like an improvement.