configs/clicker2-stm32: Fixes minor SPI configuration issues

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

realloc(): When realloc() has to fall back to calling malloc(), size including overhead was being provided to malloc(), causing a slightly larger allocation than needed.  Noted by initialkjc@yahoo.com

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.