It (-fvtable-gc semantics) wasn't implemented and (prove me
wrong) can probably not be implemented in general, but maybe
it's possible for special cases like a chain of single
inheritance. The option -fvtable-gc has been dropped from GCC,
and the pseudos are not emitted by GCC in CVS (unless that
changed in the last month, but probably not judging from Zack's
comment).
I suggest new binutils ports should not (have to) implement
support for those relocs (and support in old ports be removed
some time).