[PPL-devel] make check -n fails

Hello.

While packaging PPL for Gentoo I found that our package manager kept skipping running the testsuite. Basically, to determine if a package has a testsuite it first runs make in dry-run mode:

+ make -j1 check -n + make -j1 test -n

..and if successful it goes ahead and runs the tests.

After a bit of poking, I discovered that the problem is that running `make check -n` in PPL fails with an error:

make[3]: *** No rule to make target `../../tests/libppl_tests.a', needed by `addcongruences1'. Stop.

Regular `make check` works fine of course, as does `make check -n` after `make check`.

Full log attached. Please CC me on replies.