compiler: add missing Slice_info_expression::do_traverse

Fixes golang/go#59169

Change-Id: I980a90dab859a1a8d15992e69f1051eb4806f107
Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/478176
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
diff --git a/go/expressions.h b/go/expressions.h
index a1e3733..3d7e787 100644
--- a/go/expressions.h
+++ b/go/expressions.h
@@ -4410,6 +4410,10 @@
   { return this->slice_info_; }
 
  protected:
+  int
+  do_traverse(Traverse* traverse)
+  { return Expression::traverse(&this->slice_, traverse); }
+
   Type*
   do_type();