opensp fails to build

[Joshua Root]

Uli Wienands wrote:
> Trying to fix some (a lot of) broken ports. Running into a snag with 
> opensp, which fails to build.

Fixed:
<https://github.com/macports/macports-ports/commit/0d29c8f434da8135ac75bbed3404a6d5570fcf1f>

> This is surprising as I must have had at some point a working install of 
> it.

Likely built with g++-4.2 before the libc++ transition, or at least with
an older macports clang++.

- Josh