dev-python/construct-2.9.45 ebuild support only:

PYTHON_COMPAT=( python{2_7,3_5,3_6} )

 
Based on https://github.com/construct/construct/blob/v2.9.45/setup.py it shall support python 3.7 as well.

After modifing the ebuild, by adding

PYTHON_COMPAT=( python{2_7,3_5,3_6,3_7} )

It worked fine