[qfvis] Use cmem for portal flow stack node allocation

The portal flow stack nodes contain a simd vector, which requires
16-byte alignment. However, on 32-bit Windows, malloc returns 8-byte
aligned memory, leading to eventual segfaults. Since pstack_t is 48
bytes on 32-bit systems, it fits nicely into a 64-byte aligned cache
line (or two on 64-bit systems due to being 80 bytes).

tools/qfvis/source/flow.c

@@ -79,7 +79,7 @@ new_stack (threaddata_t *td)
 {
 	pstack_t   *stack;
 
-	stack = malloc (sizeof (pstack_t));
+	stack = cmemalloc (td->memsuper, sizeof (pstack_t));
 	stack->next = 0;
 	stack->mightsee = set_new_size_r (&td->set_pool, portalclusters);
 	td->stats.stack_alloc++;