Fork rules_cc starlark rules (and deps)

This institutes a temporary fork of
https://github.com/bazelbuild/rules_cc and one of its dependencies
(https://github.com/bazelbuild/bazel-skylib). This fork contains a
minimal set of a features to facilitate prototyping of Bazel builds of
C++ library targets and the toolchains they depend on.

At a later time, we will use a more principlied solution to pull HEAD of
these two github repositories into AOSP.

Test: Manually verified use of experimental_shared_library.bzl in a
separate prototype change.
Test: Treehugger

Change-Id: I9b35c3b15b7cce408c8e7f87e76b8e509345771a
diff --git a/common.bazelrc b/common.bazelrc
index 587862b..4a6aea9 100644
--- a/common.bazelrc
+++ b/common.bazelrc
@@ -18,6 +18,9 @@
 # Disable middleman actions
 build --noexperimental_enable_aggregating_middleman
 
+# Disable local cpp toolchain detection, as it is explicitly declared in AOSP.
+build --action_env=BAZEL_DO_NOT_DETECT_CPP_TOOLCHAIN=1
+
 # Enable building targets in //external:__subpackages__.
 common --experimental_sibling_repository_layout
 common --experimental_disable_external_package