Bazel: Export j2objc in guava library to fix build warning

Bazel correctly emits warning when the classpath contains a reference to
com.google.j2objc.annotations.ReflectionSupport, which isn't on the
classpath:

  warning: unknown enum constant ReflectionSupport$Level.FULL
    reason: class file for com.google.j2objc.annotations.ReflectionSupport$Level not found

See this issue for more details: [1].

[1] https://github.com/bazelbuild/bazel/issues/6414

Bug: Issue 9779
Change-Id: I313549d5cb219cb144087dcdc85091f21faa6e94

lib/BUILD

@@ -90,8 +90,10 @@ java_library(
     name = "guava",
     data = ["//lib:LICENSE-Apache2.0"],
     visibility = ["//visibility:public"],
-    exports = ["@guava//jar"],
-    runtime_deps = [":j2objc"],
+    exports = [
+        ":j2objc",
+        "@guava//jar",
+    ],
 )
 
 java_library(