The OLD behaviors of all policies are deprecated, but only by
documentation. Add an explicit deprecation diagnostic for policies
introduced in CMake 3.9 and below to encourage projects to port away
from setting policies to OLD.
BUILD_WITH_INSTALL_RPATH, SKIP_BUILD_RPATH, CMAKE_SKIP_RPATH and
CMAKE_SKIP_INSTALL_RPATH no longer any effect on the install name
of a target on macOS.
Fixes: #16589