am 7d1d98b9: am a02b93bd: libc: add sanity checks to pthread_mutex_destroy()

Merge commit '7d1d98b97e947de22aff4c0b67eec7ae68c822ee'

* commit '7d1d98b97e947de22aff4c0b67eec7ae68c822ee':
  libc: add sanity checks to pthread_mutex_destroy()