[Bug c++/113020] Explicit template instantiation of template specialization using a template base class fails after extern template declaration with linker error

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113020

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
The commands needed to get the link error without using cmake:
```
g++ -std=c++20   -c -o main.o main.cpp
g++ -std=c++20   -c -o base.o base.cpp
g++ -std=c++20   -c -o sub.o sub.cpp
g++ -o app main.o base.o sub.o
```