Add skylib dependency

[Copybara import of https://github.com/bazelbuild/rules_cc/pull/10]

Skylib will be used to check minimum supported Bazel version.
Merge 2e5b5eb2d0 into 3723b4c35f

PiperOrigin-RevId: 240725578

WORKSPACE

@@ -80,3 +80,6 @@ http_archive(
 load("@io_bazel_rules_go//go:deps.bzl", "go_rules_dependencies", "go_register_toolchains")
 go_rules_dependencies()
 go_register_toolchains()
+
+load("//cc:deps.bzl", "rules_cc_deps")
+rules_cc_deps()

cc/deps.bzl

@@ -0,0 +1,17 @@
+load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
+
+def rules_cc_deps():
+    _maybe(
+        http_archive,
+        name = "bazel_skylib",
+        sha256 = "2ef429f5d7ce7111263289644d233707dba35e39696377ebab8b0bc701f7818e",
+        strip_prefix = "bazel-skylib-0.8.0",
+        urls = [
+            "https://mirror.bazel.build/github.com/bazelbuild/bazel-skylib/archive/0.8.0.tar.gz",
+            "https://github.com/bazelbuild/bazel-skylib/archive/0.8.0.tar.gz",
+        ],
+    )
+
+def _maybe(repo_rule, name, **kwargs):
+    if name not in native.existing_rules():
+        repo_rule(name = name, **kwargs)