Factor out and simplify size computation.

* pgcc 20 cannot handle this steaming hot C99 material.

test/test_combinatorics_c.c

@@ -72,13 +72,14 @@ main()
   uint32_t (*occCount)[n];
 
   list = xmalloc(sizeof (list[0]) * n);
-  occCount = xmalloc(sizeof (occCount[0]) * n * n);
+  size_t occCountSize = sizeof (uint32_t) * n * n;
+  occCount = xmalloc(occCountSize);
   size_t failures;
   for (size_t repeats = 0;
        repeats < (sizeof (numRunsList)/sizeof (numRunsList[0]));
        ++repeats)
   {
-    memset(occCount, 0, sizeof (occCount[0]) * n * n);
+    memset(occCount, 0, occCountSize);
     uint32_t numRuns = numRunsList[repeats];
     for (uint32_t j = 0; j < numRuns; ++j)
     {
@@ -111,6 +112,8 @@ main()
       }
     }
   }
+  free(list);
+  free(occCount);
   return failures?EXIT_FAILURE:EXIT_SUCCESS;
 }