`cross-python` lacks support for `python_add_library`

[IsabelParedes]

PYTHON_ADD_LIBRARY is normally defined in cmake-X.XX/Modules/FindPython/Support.cmake. The custom FindPython.cmake fails to include this file.

This error shows up when downstream packages try to use this function.

- CMake Error at src/rapidfuzz/CMakeLists.txt:34 (python_add_library):
-   Unknown CMake command "python_add_library".

Current packages affected:

• Build rapidfuzz for emscripten-4x #3305
• Build segyio for emscripten-4x #3673
• Build iminuit for emscripten-4x #3654

[DerThorsten]

fixed via #3800 for 3x and #3801 for 4x