Dear Guix,

The attached two patches update python-anndata and python-scanpy, which 
effectively fix the build for python-scanpy.

python-anndata switched to a PEP518 setup instead of the regular Python 
"setup.py" approach.  So with some help on IRC, I added custom phases 
inspired by the python-tinycss2 package.

Kind regards,
Roel Janssen