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>

configs/clicker2-stm32:  Cleans up minor issues

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

Add ffsl(), ffsll(), fls(), flsl(), flsll() and use GCC's __builtin_ctz/__builtin_clz for faster implementation of these

I needed to use DS3231, I remember that in past it worked ok, but now for stm32f4xx is used another driver (chip specific, stm32f40xxx_i2c.c) and DS3231 driver doesn't work. After investigating a problem I found that I2C driver (isr routine) has a few places there it sends stop bit even if not all messages are managed. So, e.g., removing stm32_i2c_sendstop (#1744) and adding stm32_i2c_sendstart after data reading helps to make DS3231 working.  Verified by David Sidrane.

The interrupt occurs over the counter overflow

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

fix compile error when disabled the flash data cache corruption for stm32 f1xx

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

stm322_flash:missing unlock on F1 HSI off path

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