pthread mutexes:  Add option to support both unsafe and robust mutexes via pthread_mutexattr_get/setrobust().

pthreads:  Add a configuration option to disable robust mutexes and revert to the traditional unsafe mutexes.

when pthread exits or is cancelled, mutexes held by thread are marked inconsistent and the highest priority thread waiting for the mutex is awakened.

pthreads: Partial implementation of final part of robust mutexes: Keep list of all mutexes held by a thread in a list in the TCB.

pthread: Fix return value of pthread_give/takesemaphore().  Add option to pthread_takesemaphore to ignore EINTR or not.

pthreads: Add more robustness characteristics: pthread_mutex_lock() and trylock() will now return EOWNERDEAD if the mutex is locked by a thread that no longer exists.  Add pthread_mutex_consistent() to recover from this situation.

STM32 COMP cosmetics

Approved-by: Gregory Nutt <gnutt@nuttx.org>

Add COMP character driver

Approved-by: Gregory Nutt <gnutt@nuttx.org>