Re: pre-C++11 compilers

[maya%netbsd.org@localhost]

After some discussion it appears that the libstdc++.so search is based
on matching SONAME and looking based on RPATH.

So long as we specify the newest GCC lib directory first in RPATH for
all packages, we should be safe. That causes some issues with
reproducibility, there's probably a nicer way to do it.

libstdc++ does aim to be backwards compatible, so breakage should be rare.