[Regression 1.69.0] Clang UBSan triggers when std::string is used in notify()

[nafur]

We found that clang UBSan shows undefined behaviour when we use an option of type std::string with po::notify(). Please see https://stackoverflow.com/q/55064334/2375725 for more details and a minimal working example.
My colleague has already bisected the issue in this comment and it seems to be related to activating -fvisibility-inlines-hidden and -fvisibility=hidden.
Unfortunately we have no idea where to go from here...

We will also open a ticket at clang as we are really not sure whether this is a false positive in clang UBSan or actual undefined behaviour.