Libstdc++-v3 vs darwin vs weak support

[Benjamin Kosnik]

> I'd like to know from the maintainers (or other knowledgeable people) 
> which is the current situation, whether those explicit instantiations 
> are still needed. I'm asking because I mean to move from v7 to mainline 
> a bunch of similar testcases...

I think you should kill these bits, for a couple of reasons. One, I
don't know if they are necessary when using mt_alloc circa 20050315. I'm
thinking that they are not, just due to design changes. Two, mt_alloc is
not the default allocator for darwin, or for other platforms that are
hostile to weak symbols.

For full details on Darwin and weak symbols, I recommend asking Geoff Keating.

best,
benjamin

ps. I'm sure this is most relevant for AIX. Darwin was probably picked
because, at the time,  it was easier to test weak symbol support on
darwin than on AIX.