Handling C++11

[Ken Cunningham]

Well, the entire c++ library on the buildbot would have to be rebuilt
against libgcc's libstdc++ for this to work -- all of octave's deps
and deps of deps would need to be built the same as octave, of course,
and so everything else too. The whole machine has to be configured the
same way (which is why intel appears to have funded the libgcc
extensions when some linux distros went with defaulting to libgcc5+,
making clang/llvm non-functional on those distros until they fixed
it).

In the end, you would seem to wind up in a similar situation as we're
in now with libc++ on these older machines.

I guess I'm struggling with the benefit of doing this over either
fixing the metadata problem in archives and hosting libc++ files on
the buildbots, or just defaulting to libc++ on these older machines if
we're ready for that.