The addition of the TESTS knob and its enabling of the build of tests in
lib/libcrypt/tests/ broke the build. The reason is that we cannot descend
into tests/ subdirectories until all prerequisites have been built, which
in the case of tests may be "a lot of things" (libatf-c in this case).
Ensure that we do not walk tests/ directories during the bootstrapping of
the libraries as part of buildworld.
Reviewed by: freebsd-testing
Approved by: rpaulo (mentor)
eaa9118896