ThirdParty: Add optional-lite polyfill

Thanks to all who have made contributions to
https://github.com/martinmoene/optional-lite

third-party/optional-lite/BUCK

@@ -0,0 +1,11 @@
+prebuilt_cxx_library(
+  name = 'optional-lite',
+  header_namespace = '',
+  header_only = True,
+  exported_headers = subdir_glob([
+    ('include/nonstd', '**/*.hpp'),
+  ]),
+  visibility = [
+    'PUBLIC',
+  ],
+)