I've never provided any JCOV_ make variables, without having any trouble.
In jtreg-4.2-b10 I get:
make: *** No rule to make target '/lib/jcov.jar', needed by '/$DIR/build/images/jtreg/lib/jcov.jar'. Stop.
Using jcov with jtreg is underdocumented (the dependency is not listed in the README at all!), but it should be an optional dependency
In jtreg-4.2-b10 I get:
make: *** No rule to make target '/lib/jcov.jar', needed by '/$DIR/build/images/jtreg/lib/jcov.jar'. Stop.
Using jcov with jtreg is underdocumented (the dependency is not listed in the README at all!), but it should be an optional dependency