cmd/gc: do not export useless private symbols.
Fixes #4252.
R=rsc, golang-dev, mirtchovski, daniel.morsing, dave, lvd
CC=golang-dev
https://golang.org/cl/6856126
diff --git a/test/fixedbugs/issue4252.go b/test/fixedbugs/issue4252.go
new file mode 100644
index 0000000..1b0e5b2
--- /dev/null
+++ b/test/fixedbugs/issue4252.go
@@ -0,0 +1,11 @@
+// rundir
+
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Issue 4252: tests that fixing the issue still allow
+// builtins to be redeclared and are not corrupted
+// in export data.
+
+package ignored
