Fix build by invoking gfortran directly

[mgalardini]

Relatively ugly hack to allow downstream packages to use the library

I could not get f2py (numpy external modules builder) to work with glmnet_python, so I resorted to this hack, which is slightly more elegant than this other fork.

[johnlees]

That looks sensible!
Do we also want to add an ext_modules section (like this example: https://github.com/johnlees/unitig-caller/blob/master/setup.py)

[mgalardini]

Oh nice! Didn't notice that, looks much cleaner, I'll port it over and update the PR, thanks!

[mgalardini]

Seems to be working fine now, thanks again