See https://github.com/coq/coq/pull/10947 (.coqdeps.d now uses the name
of the Coq Makefile) and https://github.com/coq/coq/pull/8642 (Coq now
generates empty interface files *.vos when compiling).

thanks to Christian Doczkal <doczkal@ps.uni-saarland.de> for the Makefile snippet!

I planned to use them to simplify wsat_le, but it did not turn out to be simpler.