compiler: improve recursive type detection

Detect recursive type definition like
    "type T0 T1; type T1 T2; ...... type Tn T0".
    
    Fixes golang/go#25320.
    
    Reviewed-on: https://go-review.googlesource.com/c/159837

From-SVN: r268347

gcc/go/gofrontend/MERGE

@@ -1,4 +1,4 @@
-d67c4bf0c42b79d54925ba8c5f23278ee6c3efb6
+5ccb2d8593963e06ec3a35d362b384e82301d9f0
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

gcc/go/gofrontend/types.cc

@@ -10259,6 +10259,15 @@ Find_type_use::type(Type* type)
 	  break;
 
 	case Type::TYPE_NAMED:
+          if (type->named_type() == type->base()->named_type())
+            {
+              this->found_ = true;
+              return TRAVERSE_EXIT;
+            }
+          else
+	    go_assert(saw_errors());
+	break;
+
 	case Type::TYPE_FORWARD:
 	  go_assert(saw_errors());
 	  break;