util/util.bzl: use implementation_deps to hide internal header

Change-Id: I34b81a96e93b1475ae9a8f6ff8201edaab52b3f1
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/83387
Reviewed-by: David Benjamin <davidben@google.com>
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: Adam Langley <agl@google.com>

util/util.bzl

diff --git a/util/util.bzl b/util/util.bzl
index 6b5b750..9da4320 100644
--- a/util/util.bzl
+++ b/util/util.bzl
@@ -168,7 +168,8 @@
         cc_library(
             name = name,
             hdrs = hdrs,
-            deps = [":" + name_internal],
+            includes = includes,
+            implementation_deps = [":" + name_internal],
             visibility = visibility,
         )