Bazel: Don't depend directly on @local_jdk in java_doc rule

To support alternative java_toolchains (e.g.: to activate all error
prone warnings) we should not directly depend on @local_jdk, but use
@bazel_tools//tools/jdk:current_java_runtime to get the configured JDK
instead.

See this issue for more context: [1].

[1] https://github.com/bazelbuild/bazel/issues/5997

Inspired-by: Liam Miller-Cushon <cushon@google.com>
Bug: Issue https://github.com/GerritCodeReview/gitiles/issues/1
Change-Id: I87cde26cddfeaa317e6489e2c5cdcceb054c670d
diff --git a/tools/javadoc.bzl b/tools/javadoc.bzl
index 43346ba..744caf4 100644
--- a/tools/javadoc.bzl
+++ b/tools/javadoc.bzl
@@ -34,7 +34,7 @@
         "rm -rf %s" % dir,
         "mkdir %s" % dir,
         " ".join([
-            ctx.file._javadoc.path,
+            "%s/bin/javadoc" % ctx.attr._jdk[java_common.JavaRuntimeInfo].java_home,
             "-Xdoclint:-missing",
             "-protected",
             "-encoding UTF-8",
@@ -65,14 +65,10 @@
         "pkgs": attr.string_list(),
         "title": attr.string(),
         "external_docs": attr.string_list(),
-        "_javadoc": attr.label(
-            default = Label("@local_jdk//:bin/javadoc"),
-            single_file = True,
-            allow_files = True,
-        ),
         "_jdk": attr.label(
-            default = Label("@local_jdk//:jdk-default"),
+            default = Label("@bazel_tools//tools/jdk:current_java_runtime"),
             allow_files = True,
+            providers = [java_common.JavaRuntimeInfo],
         ),
     },
     outputs = {"zip": "%{name}.zip"},