compiler: Check for errors in the underlying types of unary expressions.

    
    Fixes golang/go#11592.
    
    Reviewed-on: https://go-review.googlesource.com/12044

From-SVN: r226122

gcc/go/gofrontend/MERGE

-5c49a77455f52ba2c7eddb5b831456dc1c67b02f
+b4a932b4a51b612cadcec93a83f94d6ee7d7d190
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

gcc/go/gofrontend/expressions.cc

@@ -3955,6 +3955,8 @@ Unary_expression::do_check_types(Gogo*)
       // Indirecting through a pointer.
       if (type->points_to() == NULL)
 	this->report_error(_("expected pointer"));
+      if (type->points_to()->is_error())
+	this->set_is_error();
       break;
 
     default: