lang/gcc* broken on current, fix in the works

From: Brooks Davis <brooks_at_freebsd.org>
Date: Wed, 07 Feb 2024 05:55:48 UTC 
A late breaking change to my libsys patch caused the MULTILIB option to
be broken on current.  I've got a fix that seems to be working, but want
to do a bit more testing before I commit it as breaking pthreads broadly
(vs linkage with GNU ld) would be very bad.

For now you can disable MULTILIB as a workaround.

Sorry for the breakage.

-- Brooks