Add libunwind third-party package

Summary:
X-link: pytorch/executorch#3708

X-link: facebook/folly#2213

Reviewed By: yfeldblum

Differential Revision: D57680723

Pulled By: bigfootjon

fbshipit-source-id: ebe210099952d496e0315ede712da9941338edd8

shim/third-party/libunwind/BUCK

@@ -0,0 +1,15 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+#
+# This source code is licensed under both the MIT license found in the
+# LICENSE-MIT file in the root directory of this source tree and the Apache
+# License, Version 2.0 found in the LICENSE-APACHE file in the root directory
+# of this source tree.
+
+load("@shim//third-party:third_party.bzl", "third_party_library")
+
+oncall("open_source")
+
+third_party_library(
+    name = "unwind",
+    pkgconfig_name = "libunwind",
+)