compiler: unalias receiver type in export data

Test case is https://golang.org/cl/292009.

Change-Id: I21cc1f4040bf283bc6d376ec026bdd216d915d58
Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/291991
Trust: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

go/gogo.cc

diff --git a/go/gogo.cc b/go/gogo.cc
index 62b06be..38a2f6f 100644
--- a/go/gogo.cc
+++ b/go/gogo.cc
@@ -5898,7 +5898,7 @@
       exp->write_name(receiver->name());
       exp->write_escape(receiver->note());
       exp->write_c_string(" ");
-      exp->write_type(receiver->type());
+      exp->write_type(receiver->type()->unalias());
       exp->write_c_string(") ");
     }