Completes the Implementation of the TLS-based errno

- Remove per-thread errno from the TCB structure (pterrno)
- Remove get_errno() and set_errno() as functions.  The macros are still available as stubs and will be needed in the future if we need to access the errno from a different address environment (KERNEL mode).
- Add errno value to the tls_info_s structure definitions
- Move sched/errno to libs/libc/errno.  Replace old TCB access to the errno with TLS access to the errno.

sched/mqueue/mq_rcvinternal.c

@@ -157,20 +157,17 @@ int nxmq_wait_receive(mqd_t mqdes, FAR struct mqueue_msg_s **rcvmsg)
 
       if ((mqdes->oflags & O_NONBLOCK) == 0)
         {
-          int saved_errno;
-
           /* Yes.. Block and try again */
 
           rtcb           = this_task();
           rtcb->msgwaitq = msgq;
           msgq->nwaitnotempty++;
 
-          /* "Borrow" the per-task errno to communication wake-up error
+          /* Initialize the 'errcode" used to communication wake-up error
            * conditions.
            */
 
-          saved_errno    = rtcb->pterrno;
-          rtcb->pterrno  = OK;
+          rtcb->errcode  = OK;
 
           /* Make sure this is not the idle task, descheduling that
            * isn't going to end well.
@@ -185,9 +182,7 @@ int nxmq_wait_receive(mqd_t mqdes, FAR struct mqueue_msg_s **rcvmsg)
            * errno value (should be either EINTR or ETIMEDOUT).
            */
 
-          ret            = rtcb->pterrno;
-          rtcb->pterrno  = saved_errno;
-
+          ret = rtcb->errcode;
           if (ret != OK)
             {
               return -ret;

sched/mqueue/mq_sndinternal.c

@@ -260,8 +260,6 @@ int nxmq_wait_send(mqd_t mqdes)
 
           while (msgq->nmsgs >= msgq->maxmsgs)
             {
-              int saved_errno;
-
               /* Block until the message queue is no longer full.
                * When we are unblocked, we will try again
                */
@@ -270,12 +268,11 @@ int nxmq_wait_send(mqd_t mqdes)
               rtcb->msgwaitq = msgq;
               msgq->nwaitnotfull++;
 
-              /* "Borrow" the per-task errno to communication wake-up error
+              /* Initialize the errcode used to communication wake-up error
                * conditions.
                */
 
-              saved_errno   = rtcb->pterrno;
-              rtcb->pterrno = OK;
+              rtcb->errcode = OK;
 
               /* Make sure this is not the idle task, descheduling that
                * isn't going to end well.
@@ -290,9 +287,7 @@ int nxmq_wait_send(mqd_t mqdes)
                * per-task errno value (should be EINTR or ETIMEOUT).
                */
 
-              ret           = rtcb->pterrno;
-              rtcb->pterrno = saved_errno;
-
+              ret = rtcb->errcode;
               if (ret != OK)
                 {
                   return -ret;

sched/mqueue/mq_waitirq.c

@@ -97,9 +97,9 @@ void nxmq_wait_irq(FAR struct tcb_s *wtcb, int errcode)
           msgq->nwaitnotfull--;
         }
 
-      /* Mark the errno value for the thread. */
+      /* Mark the error value for the thread. */
 
-      wtcb->pterrno = errcode;
+      wtcb->errcode = errcode;
 
       /* Restart the task. */