third_party/cap: initialize

This adds libcap which is needed for any chance at running chrony as non-root.

Upstream contains a multi-stage codegen based on various external utilities
which has been replaced by a clean Go script. Upstream is capable of also
using gperf to generate hash tables for faster lookups, but due to the
extremely low amount of items (~40) and the additional complexity this is
not enabled.

This is not tested standalone, but it has been tested with chrony.

Change-Id: I638f6aea98158cd2e2838531a5a6125e724838f5
Reviewed-on: https://review.monogon.dev/c/monogon/+/317
Reviewed-by: Sergiusz Bazanski <serge@monogon.tech>
diff --git a/WORKSPACE b/WORKSPACE
index 5bd45f7..4ccbb9e 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -202,6 +202,13 @@
     name = "chrony",
 )
 
+load("//third_party/cap:external.bzl", "cap_external")
+
+cap_external(
+    name = "cap",
+    version = "1.2.55",
+)
+
 register_toolchains("//:host_python")
 
 # python dependencies. Currently we don't use Python, but some of our deps (ie. gvisor) do expect @pydeps// to exist, even