C++: Fix @rules_cc for toolchain type in cc_shared_library

We need @rules_cc in front of the toolchain type in cc_shared_library. This is
still experimental.

More complete test suite is on the way in a separate CL I'm working on.

RELNOTES:none
PiperOrigin-RevId: 282716323
Change-Id: I797ef08f18987adef82b7c7d484e2838f4e1ba6a
diff --git a/examples/experimental_cc_shared_library.bzl b/examples/experimental_cc_shared_library.bzl
index bc5285a..8c21896 100644
--- a/examples/experimental_cc_shared_library.bzl
+++ b/examples/experimental_cc_shared_library.bzl
@@ -273,6 +273,6 @@
         "exports": attr.label_list(aspects = [graph_structure_aspect]),
         "_cc_toolchain": attr.label(default = "@bazel_tools//tools/cpp:current_cc_toolchain"),
     },
-    toolchains = ["//cc:toolchain_type"],
+    toolchains = ["@rules_cc//cc:toolchain_type"],  # copybara-use-repo-external-label
     fragments = ["cpp"],
 )