Changes to compile with gcc 4.6

Change-Id: I55908b3b98b49373ce948fd1f12e0a5cd56ae4f7
diff --git a/src/dex2oat.cc b/src/dex2oat.cc
index 2781aae..41adc74 100644
--- a/src/dex2oat.cc
+++ b/src/dex2oat.cc
@@ -574,7 +574,7 @@
       UniquePtr<ZipArchive> zip_archive(ZipArchive::OpenFromFd(zip_fd));
       if (zip_archive.get() == NULL) {
         LOG(ERROR) << "Failed to zip from file descriptor for " << zip_name;
-        return NULL;
+        return EXIT_FAILURE;
       }
       const DexFile* dex_file = DexFile::Open(*zip_archive.get(), zip_name);
       if (dex_file == NULL) {