Typedefs starting with `u' in osfmk/kern

• Ulock osfmk/kern/sync_lock.h:62
• ulock_t osfmk/kern/sync_lock.h:64
• usimple_lock_t osfmk/kern/simple_lock_types.h:194
• uslock_debug osfmk/kern/simple_lock_types.h:184