Ever since statically linking Qt, we've been linking the C++ library
statically too (-static-libstdc++). Take this into
account in the symbol checker.
This is a partial backport of [[https://github.com/bitcoin/bitcoin/pull/17569 | core#17569]]
https://github.com/bitcoin/bitcoin/pull/17569/commits/b77d5ad59fb9f3f26d919ee6c33ae732382de504