Make libstdc++ loading more reliable

[gbaraldi]

We currently load the libstdc++ we ship from rpath, which is usually fine. It isn't fine when the system's libstdc++ is newer than ours, and a system lib needs the newer symbols, which leads to errors.
To fix that there needs to be some way that checks the systems libstdc++ and ,if it's newer than ours, load it instead.

Some ideas were put forward in the ci-dev call.

• remove it from the rpath and dlopen it. Check for some GLIBCXX version symbol and if it's there then load it. Otherwise dlclose it and load ours as usual (Probably the best)
• Do the same thing but on an external process if dlclose causes issues.