am a02b93bd: libc: add sanity checks to pthread_mutex_destroy()

Merge commit 'a02b93bd75a9d156117264d88069566e447397e2' into gingerbread-plus-aosp

* commit 'a02b93bd75a9d156117264d88069566e447397e2':
  libc: add sanity checks to pthread_mutex_destroy()