Pybind11: Using pybind with existing CMake structure

[JohnV7]

Issue description

I'm trying to use pybind with an existinc cmake structure. I modified the existing CMakeLists.txt file adding
add_subdirectory(src/pybind11)
pybind11_add_module(mycode src/mycode.cpp)
target_link_libraries(mycode PRIVATE ${MYCODE_LIBRARIES})

This compiles succesfully and generates mycode.so, but when trying to import it via python I get following error:
import mycode

ImportError: ./mycode.so: undefined symbol: PyInstanceMethod_Type

Any ideas what the problem may be?

[Xfel]

This might come from a python version mismatch between the version used to compile and the version used to run.

[henryiii]

Should be fixed by #2370 and related changes.