fix: conda-forge patch

[henryiii]

Conda forge adds a special "Library" prefix to the library location on Windows, see the docs:

Unix-style packages on Windows, which are usually statically linked to executables, are built in a special Library directory under the build prefix. The environment variables listed in the following table are defined only on Windows.

See conda-forge/pybind11-feedstock#52

This provides a hook to this for systems like conda-forge.