threads: don't join thread if pthread_create failed; fix error messages

lib/src/common/threads.c

@@ -146,18 +146,17 @@ bool threads_new_rt_cpu(pthread_t* thread, void* (*start_routine)(void*), void*
   int err = pthread_create(thread, attr_enable ? &attr : NULL, start_routine, arg);
   if (err) {
     if (EPERM == err) {
-      // Join failed thread for avoiding memory leak from previous trial
-      pthread_join(*thread, NULL);
-
-      perror("Warning: Failed to create thread with real-time priority. Creating it with normal priority");
+      fprintf(stderr,
+              "Warning: Failed to create thread with real-time priority. Creating it with normal priority: %s\n",
+              strerror(err));
       err = pthread_create(thread, NULL, start_routine, arg);
       if (err) {
-        perror("pthread_create");
+        fprintf(stderr, "Error: Failed to create thread with normal priority: %s\n", strerror(err));
       } else {
         ret = true;
       }
     } else {
-      perror("pthread_create");
+      fprintf(stderr, "Error: Failed to create thread with real-time priority: %s\n", strerror(err));
     }
   } else {
     ret = true;