vvp: fail gracefully on multi-bit modpath delays (issue #1184)

The code doesn't currently handle the case of different bits within
the vector needing different delays (e.g. when the rise and fall
delays are different and some bits are rising as other bits are
falling) and aborts with an assertion failure. For now, output a
suitable "sorry" message and exit gracefully.

vvp/delay.cc

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2005-2021 Stephen Williams <[email protected]>
+ * Copyright (c) 2005-2024 Stephen Williams <[email protected]>
  *
  *    This source code is free software; you can redistribute it
  *    and/or modify it in source code form under the terms of the GNU
@@ -664,7 +664,11 @@ void vvp_fun_modpath::recv_vec4(vvp_net_ptr_t port, const vvp_vector4_t&bit,
 	      /* If the current and new bit values match then no delay
 	       * is needed for this bit. */
 	    if (cur_vec4_.value(idx) == bit.value(idx)) continue;
-	    assert(tmp == use_delay);
+	    if (tmp != use_delay) {
+                  fprintf(stderr, "sorry: multi-bit module path delays are "
+                                  "currently not fully supported.\n");
+                  exit(2);
+            }
       }
 
       cur_vec4_ = bit;