[fuchsia] Add a BUILD.gn file

This file will let us build this library using the Fuchsia build system.

Change-Id: I5150b41db3f4a9e1d402ecf9e67fff0e4215be89
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/android.googlesource.com/platform/system/libbase/+/473860
Reviewed-by: Steve Austin <steveaustin@google.com>
diff --git a/BUILD.gn b/BUILD.gn
new file mode 100644
index 0000000..e28e9cb
--- /dev/null
+++ b/BUILD.gn
@@ -0,0 +1,11 @@
+# Copyright 2021 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.
+
+config("headers") {
+  include_dirs = [ "include" ]
+}
+
+source_set("libbase") {
+  public_configs = [ ":headers" ]
+}