Add BUILD.gn file.

Change-Id: I556c51261156e01e9b62d759e0760829e3195c4a
diff --git a/BUILD.gn b/BUILD.gn
new file mode 100644
index 0000000..9e04c2a
--- /dev/null
+++ b/BUILD.gn
@@ -0,0 +1,10 @@
+# Copyright 2017 The Fuchsia Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+source_set("murmurhash") {
+  sources = [
+    "murmurhash.c",
+    "murmurhash.h",
+  ]
+}