POSIX says pthread_mutex_trylock returns EBUSY, not EDEADLK.

Found by unit test.

Change-Id: Iffbd2f04213616927fbd7b5419460031f7a078e9
Fix the type of u_ar0 in <sys/user.h>.

Change-Id: I9332dea60f7c60b45bc80026686c266bfa7a782c
Merge "POSIX says pthread_mutex_trylock returns EBUSY, not EDEADLK."
Merge "Fix the type of u_ar0 in <sys/user.h>."