[Bug libffi/84410] libffi doesn't support riscv now, but not disabled in configure.ac

[sch...@linux-m68k.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84410

--- Comment #3 from Andreas Schwab <sch...@linux-m68k.org> ---
The latest commit in <https://github.com/libffi/libffi/pull/281> is working
well.