Empty class passing

[Jason Merrill]

>>>>> "Mark" == Mark Mitchell <mark at codesourcery.com> writes:

> In particular, after polling lots of C++ experts, it turns out that
> nobody cares about optimizing empty class passing.

Nobody may care in the abstract, but STL uses empty classes quite a bit
(for iterator tags), and passes them to functions, so I still think it's
useful to optimize.  But perhaps not in a way that affects the ABI; your
change sounds fine to me.

Jason