treewide: setup libelf build

Change-Id: I42ead2eac3be455015a302f947dfcc311057e46e
Reviewed-on: https://review.monogon.dev/c/monogon/+/4097
Tested-by: Jenkins CI
Reviewed-by: Jan Schär <jan@monogon.tech>
diff --git a/third_party/BUILD.bazel b/third_party/BUILD.bazel
index 80b8cfb..7a1c6c1 100644
--- a/third_party/BUILD.bazel
+++ b/third_party/BUILD.bazel
@@ -24,3 +24,9 @@
     actual = "@zlib",
     visibility = ["//visibility:public"],
 )
+
+alias(
+    name = "zstd",
+    actual = "@zstd//:zstd",
+    visibility = ["//visibility:public"],
+)