CMake has a surprising default behavior where looking up a library by
multiple names gives the name order higher priority than the directory
search order.
For example, if your system provides "llvm-config-14" and
CMAKE_PREFIX_PATH includes "llvm-config", CMake will always end up
choosing the system-provided llvm-config-14.
This change add NAMES_PER_DIR to request the more sensible behavior:
directory search order has higher priority than name order, so
CMAKE_PREFIX_PATH always wins over system-provided tools/libraries.
dd70336f3a