config-ml.in has some logic to disable multilibs if the 64bit
libraries cannot be built. This did work until libgcc was moved to
the toplevel, now the check is used for a 64bit libgcc multilib as
well, and fails because libgcc isn't yet built. However the failure is
hidden because in the inner case statement the value for the multilib
option is tested instead of the multilib dir and the 64bit multilib
libgcc is built anyway. Other biarch platforms don't check, so is it
ok to remove the checks for sparc and mips as well?