[Bug c++/87847] spec_hasher::hash does not match with spec_hasher::equal

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87847

--- Comment #4 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Or maybe just

@@ -1879,6 +1888,9 @@ iterative_hash_template_arg (tree arg, hashval_t val)
    return val;
       }

+    case TEMPLATE_TEMPLATE_PARM:
+      return val;
+
     default:
       break;
     }