fix constraint violation in qsort wrapper around qsort_r

function pointer types do not implicitly convert to void *. a cast is
required here.

src/stdlib/qsort_nr.c

@@ -10,5 +10,5 @@ static int wrapper_cmp(const void *v1, const void *v2, void *cmp)
 
 void qsort(void *base, size_t nel, size_t width, cmpfun cmp)
 {
-	__qsort_r(base, nel, width, wrapper_cmp, cmp);
+	__qsort_r(base, nel, width, wrapper_cmp, (void *)cmp);
 }