The interface of the function `search_include_directories` has changed
in Cython 3.0a7 in https://github.com/cython/cython/commit/f3f7b612.
This updates the replacement used by wendelin so that it works for
both newer and older versions.

Note that wendelin.core still does not work with Cython >= 3, as that
version refuses to compile Python functions that can throw C++
exceptions (apparently, mixing C++ exceptions and Cython-generated
code is not considered safe).

/reviewed-by @kirr
/reviewed-on nexedi/wendelin.core!24