Keep expression width when evaluating expressions ahead of time.

Added 'expr_wid' parameter to calls to 'eval_expr()' within
PEBinary::elaborate_eval_expr_base_()'.  This makes a specific problem
go away and may even be the correct thing to do.

elab_expr.cc

@@ -314,8 +314,8 @@ NetExpr* PEBinary::elaborate_eval_expr_base_(Design*des,
 {
 	/* If either expression can be evaluated ahead of time, then
 	   do so. This can prove helpful later. */
-      eval_expr(lp);
-      eval_expr(rp);
+      eval_expr(lp, expr_wid);
+      eval_expr(rp, expr_wid);
 
       return elaborate_expr_base_(des, lp, rp, expr_wid);
 }