Modify the condition for ignoring compiler warning for the cast operation.

Before modification: Compiler warning was ignored only on MinGW64
After modification: Compiler warning is ignored on MinGW32 and MinGW64
Reason of modification: The cast warning here is unavoidable not only on MinGW64 but also on MinGW32.
"__GNUC__" macro is used because MSVC does not recognize this #pragma directive.

Author: watsk

portable/MSVC-MingW/port.c

@@ -247,15 +247,15 @@ StackType_t * pxPortInitialiseStack( StackType_t * pxTopOfStack,
                                                NULL ); /* No name. */
 
 
-#ifdef 	__x86_64__
-    /* MinGW-w64 compiler reports the warning for the cast operation from TaskFunction_t to LPTHREAD_START_ROUTINE. */
+#ifdef __GNUC__
+    /* GCC reports the warning for the cast operation from TaskFunction_t to LPTHREAD_START_ROUTINE. */
     /* Disable this warning here by the #pragma option. */
 #pragma GCC diagnostic push
 #pragma GCC diagnostic ignored "-Wcast-function-type"
 #endif
     /* Create the thread itself. */
     pxThreadState->pvThread = CreateThread( NULL, xStackSize, ( LPTHREAD_START_ROUTINE ) pxCode, pvParameters, CREATE_SUSPENDED | STACK_SIZE_PARAM_IS_A_RESERVATION, NULL );
-#ifdef 	__x86_64__
+#ifdef __GNUC__
 #pragma GCC diagnostic pop
 #endif