compiler: Verify pointer type's underlying type.

Fixes golang/go#11547.
    
    Reviewed-on: https://go-review.googlesource.com/13031

From-SVN: r226598

gcc/go/gofrontend/MERGE

@@ -1,4 +1,4 @@
-df080adb06f0e423820f3f6b9604b0c1093ff20a
+6fb7c3509a4eda7d2403900981b53029d6727037
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

gcc/go/gofrontend/types.h

@@ -2032,6 +2032,10 @@ class Pointer_type : public Type
   int
   do_traverse(Traverse*);
 
+  bool
+  do_verify()
+  { return this->to_type_->verify(); }
+
   bool
   do_has_pointer() const
   { return true; }