Let pthread_mutex_init() macro return 0 on Windows
mysql_priv.h:
  Return type is to be 'my_bool' for 'opt_enable_shared_memory'


sql/mysql_priv.h:
  Return type is to be 'my_bool' for 'opt_enable_shared_memory'
include/my_pthread.h:
  Let pthread_mutex_init() macro return 0 on Windows