It's masked in Gentoo and no longer needed by ipython. We can deal
with the SPKG for a few weeks until the Sage packaging catches up.
--with-system-arb=force \
--with-system-asttokens=force \
--with-system-attrs=force \
--with-system-arb=force \
--with-system-asttokens=force \
--with-system-attrs=force \
- --with-system-backcall=force \
--with-system-beniget=force \
--with-system-boost_cropped=force \
--with-system-brial=force \
--with-system-beniget=force \
--with-system-boost_cropped=force \
--with-system-brial=force \