bpo-44689: ctypes.util.find_library() now finds macOS 11+ system libraries when built on older macOS systems (GH-27251) (GH-28054)

Previously, when built on older macOS systems, `find_library` was not able to find macOS system libraries when running on Big Sur due to changes in how system libraries are stored.
(cherry picked from commit 71853a73024a98aa38a3c0444fe364dbd9709134)

Co-authored-by: Tobias Bergkvist <tobias@bergkv.ist>