Include patch to enable build on clang+libstdc++

@akraszna added a patch in the externals a while ago to make Acts build on the clang+libstdc++ build that they're rolling. We use a custom Ubuntu image which builds on clang+libc++ specifically to avoid this issue.

Officially, as far as I know, building with the combination this ATLAS build does is not supported, but I guess there's no harm in upstreaming the patch to make life a bit easier. Let's see how this affects our CI.