Expose LHAPDF_PYTHONPATH as a configure-time environment variable
Expose LHAPDF_PYTHONPATH as a configure-time environment variable for overriding the calculated install path.
Should help @ArjunBoi with overriding the weird/wrong Python sysconfig
paths returned from GitLab CI's MacOS runners with Homebrew Python, e.g. LHAPDF_PYTHONPATH=/foo/lib/python3.2.1/site-packages ./configure --prefix=/foo