Merge pull request #13963 from evedon/warnings

Fix ThisThread warnings

Author: 0xc0170

rtos/source/ThisThread.cpp

@@ -223,6 +223,7 @@ void ThisThread::sleep_for(Clock::duration_u32 rel_time)
 #if MBED_CONF_RTOS_PRESENT
     osStatus_t status = osDelay(rel_time.count());
     MBED_ASSERT(status == osOK);
+    (void) status;
 #else
     thread_sleep_for(rel_time.count());
 #endif
@@ -242,10 +243,12 @@ void ThisThread::sleep_until(Clock::time_point abs_time)
         if (abs_time - now > wait_for_u32_max) {
             osStatus_t status = osDelay(wait_for_u32_max.count());
             MBED_ASSERT(status == osOK);
+            (void) status;
             continue;
         } else {
             osStatus_t status = osDelay((abs_time - now).count());
             MBED_ASSERT(status == osOK);
+            (void) status;
             break;
         }
     }