As CGAL is `REQUIRED` in `find_package`, no test of `CGAL_FOUND` can be done, if `CGAL_FOUND` is not `TRUE`, then CMake stops with a hard error at the line `find_package(CGAL REQUIRED ...)`.
As CGAL is `REQUIRED` in `find_package`, no test of `CGAL_FOUND` can be done, if `CGAL_FOUND` is not `TRUE`, then CMake stops with a hard error at the line `find_package(CGAL REQUIRED ...)`.