POSIX Simulator: Assert if vPortYield called from a non-FreeRTOS thread (#1247)

portable/ThirdParty/GCC/Posix/port.c

diff --git a/portable/ThirdParty/GCC/Posix/port.c b/portable/ThirdParty/GCC/Posix/port.c
index ff386ac..1153e7f 100644
--- a/portable/ThirdParty/GCC/Posix/port.c
+++ b/portable/ThirdParty/GCC/Posix/port.c
@@ -384,6 +384,10 @@
 
 void vPortYield( void )
 {
+    /* This must never be called from outside of a FreeRTOS-owned thread, or
+     * the thread could get stuck in a suspended state. */
+    configASSERT( prvIsFreeRTOSThread() == pdTRUE );
+
     vPortEnterCritical();
 
     prvPortYieldFromISR();