bazel: explicitly load C++ rules

Starting with Bazel 3.0, C++ rules will require loads. See
https://github.com/bazelbuild/bazel/issues/8743

Thanks to Yannic Bonenberger for noting this in
https://boringssl-review.googlesource.com/c/boringssl/+/39825

Change-Id: I8e274c82ade6c7ec569989026190f6a0a88b47ed
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/39924
Commit-Queue: David Benjamin <davidben@google.com>
Reviewed-by: David Benjamin <davidben@google.com>
diff --git a/util/BUILD.toplevel b/util/BUILD.toplevel
index d7c731b..cba9ccb 100644
--- a/util/BUILD.toplevel
+++ b/util/BUILD.toplevel
@@ -16,6 +16,8 @@
 
 exports_files(["LICENSE"])
 
+load("@rules_cc//cc:defs.bzl", "cc_binary", "cc_library")
+
 load(
     ":BUILD.generated.bzl",
     "crypto_headers",