Handle duplicate set of global_token_order in ill-formed cases, closes #1130

Author: hsutter

source/lex.h

@@ -314,11 +314,13 @@ class token
         }
     }
 
-    auto set_global_token_order(index_t fp) const
+    auto set_global_token_order(index_t& counter) const
         -> void
     {
-        assert(global_token_order == 0);    // we only expect to set this once
-        global_token_order = fp;
+        //  In a well-formed program we only expect to set this once
+        if (global_token_order == 0) {
+            global_token_order = ++counter;
+        }
     }
 
     auto get_global_token_order() const

source/sema.h

@@ -2439,7 +2439,7 @@ class sema
     {
         //  By giving tokens an order during sema
         //  generated code can be equally checked
-        t.set_global_token_order( global_token_counter++ );
+        t.set_global_token_order( global_token_counter );
 
         auto guard = finally([&]() {
             prev2_token = prev_token;