Skip User Package Registry in find_package() calls.

In some cases, for example to locate only system wide installations, it is not desirable to use the User Package Registry when searching for packages. If the CMAKE_FIND_PACKAGE_NO_PACKAGE_REGISTRY variable is enabled, all the find_package() commands will skip the User Package Registry as if they were called with the NO_CMAKE_PACKAGE_REGISTRY argument.

See also Disabling the Package Registry.