feat(rt/posix): Added FreeRTOS-Plus-POSIX message queues implementation

Note: The current mq_open() implementation is changed to match
      the POSIX standard.

examples/system/rt_mqueue/main/posix_mqueue_example_main.c

@@ -0,0 +1,101 @@
+/*
+ * SPDX-FileCopyrightText: 2024 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Unlicense OR CC0-1.0
+ */
+
+#include <stdio.h>
+#include <fcntl.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#include <stdbool.h>
+#include <pthread.h>
+#include <mqueue.h>
+#include <string.h>
+#include <errno.h>
+#include <stdlib.h>
+
+static int s_counter = 0;
+
+const unsigned int MSG_PRIO = 0;
+
+static void *sender_function(void * arg)
+{
+    mqd_t *write_descr = (mqd_t*) arg;
+
+    while (true) {
+        printf("sending: %d\n", s_counter);
+        int result = mq_send(*write_descr, (const char*) &s_counter, sizeof(s_counter), MSG_PRIO);
+        if (result != 0) {
+            perror("Sending failed");
+            abort();
+        }
+
+        s_counter++;
+        sleep(1);
+    }
+
+    return NULL;
+}
+
+static void *receiver_function(void * arg)
+{
+    mqd_t *read_descr = (mqd_t*) arg;
+
+    while (true) {
+        int msg;
+        int result = mq_receive(*read_descr, (char*) &msg, sizeof(msg), NULL);
+        if (result == -1) {
+            perror("Sending failed");
+            abort();
+        }
+
+        printf("received: %d\n", msg);
+    }
+
+    return NULL;
+}
+
+void app_main(void)
+{
+    mqd_t write_descr;
+    mqd_t read_descr;
+    pthread_t sender;
+    pthread_t receiver;
+
+    struct mq_attr configuration = {
+        .mq_flags = 0, // ignored by mq_open
+        .mq_maxmsg = 10,
+        .mq_msgsize = sizeof(int),
+        .mq_curmsgs = 0 // ignored by mq_open
+    };
+
+    write_descr = mq_open("/my_queue", O_CREAT | O_WRONLY, S_IRUSR | S_IWUSR , &configuration);
+    if (write_descr == (mqd_t) -1) {
+        perror("Creating message queue failed");
+        abort();
+    }
+
+    read_descr = mq_open("/my_queue", O_RDONLY);
+    if (read_descr == (mqd_t) -1) {
+        perror("Opening message queue for reading failed");
+        abort();
+    }
+
+    int result;
+    result = pthread_create(&sender, NULL, sender_function, &write_descr);
+    if (result != 0) {
+        printf("Creating sender thread failed: %s", strerror(errno));
+        abort();
+    }
+
+    result = pthread_create(&receiver, NULL, receiver_function, &read_descr);
+    if (result != 0) {
+        printf("Creating receiver thread failed: %s", strerror(errno));
+        abort();
+    }
+
+    while (true) {
+        sleep(1000);
+    }
+}