Fail install if dependencies are not found.
Fail install if dependencies are not found.

The default simply does nothing, so you could build and not link with
the required libraries leaving the Python extensions broken.

SHTOOLS/SHTOOLS,MMesch/SHTOOLS,ioshchepkov/SHTOOLS,MarkWieczorek/SHTOOLS,MarkWieczorek/SHTOOLS,SHTOOLS/SHTOOLS