Expression With Possibly No Effect

In the keil_8051/9.60 compiler, this code:

void *list_traverse(void *arg) {
 void *result = NULL;
 (void)arg;

 return result;
}

generates the warning: 

*** WARNING C275 IN LINE 124 OF C:\...\list.c: expression with possibly no effect

My understanding that with most compilers, the (void)arg construct specifically indicates that arg is to be ignored.

With the Keil compiler, what's the correct way to inhibit this warning?