Add missing include guard to zip_writer.h

src/google/protobuf/compiler/zip_writer.h

diff --git a/src/google/protobuf/compiler/zip_writer.h b/src/google/protobuf/compiler/zip_writer.h
index a99bb78..9f56d68 100644
--- a/src/google/protobuf/compiler/zip_writer.h
+++ b/src/google/protobuf/compiler/zip_writer.h
@@ -60,6 +60,9 @@
 
 // Author: kenton@google.com (Kenton Varda)
 
+#ifndef GOOGLE_PROTOBUF_COMPILER_ZIP_WRITER_H__
+#define GOOGLE_PROTOBUF_COMPILER_ZIP_WRITER_H__
+
 #include <vector>
 #include <google/protobuf/stubs/common.h>
 #include <google/protobuf/io/zero_copy_stream.h>
@@ -91,3 +94,5 @@
 }  // namespace compiler
 }  // namespace protobuf
 }  // namespace google
+
+#endif  // GOOGLE_PROTOBUF_COMPILER_ZIP_WRITER_H__