compiler: ignore aliases in fieldtrack info

We want to track references to fields in the real struct, not in
aliases to the struct.

Change-Id: I9d33a7dad0d6ebaf37186cf3b64a634194532569
Reviewed-on: https://go-review.googlesource.com/96816
Reviewed-by: Damien Neil <dneil@google.com>
diff --git a/go/expressions.cc b/go/expressions.cc
index 9792faa..10ab5b5 100644
--- a/go/expressions.cc
+++ b/go/expressions.cc
@@ -11696,7 +11696,7 @@
   Location loc = this->location();
 
   std::string s = "fieldtrack \"";
-  Named_type* nt = this->expr_->type()->named_type();
+  Named_type* nt = this->expr_->type()->unalias()->named_type();
   if (nt == NULL || nt->named_object()->package() == NULL)
     s.append(gogo->pkgpath());
   else