Without going through an intricate dance with git to change the remote
URL of a repository, it's simplest to just nuke the cloned folder, as
we have to do a clean clone anyway.
Pulling in latest changes from VVL
Use BUILD_TESTS instead of VUL_TESTS. While it's good practice to
prefix variable names it makes updating this code more difficult.
Also since tests can only ever be enabled if the project is top
level, it doesn't affect add_subdirectory users.
Other misc. CMake cleanup