Cannot build :protobuf_java with Java 9

[davido]

//CC @cushon @jart

Gerrit Code Review depends on rules_closure, that started to build protobuf_java from source in their build tool chain very recently.

This building of :protobuf_java from source broke Java 9 build support in gerrit ;-(

To reproduce, install the most recent Bazel version: 0.10.rc8, or build Bazel from source, then run in protobuf@HEAD (b718551):

$ bazel --host_javabase=/usr/lib64/jvm/java-9-openjdk build --java_toolchain=@bazel_tools//tools/jdk:toolchain_jdk9 :protobuf_java
...........
INFO: Analysed target //:protobuf_java (10 packages loaded).
INFO: Found 1 target...
INFO: From Executing genrule @bazel_tools//tools/jdk:gen_platformclasspath [for host]:
Note: external/bazel_tools/tools/jdk/DumpPlatformClassPath.java uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.
ERROR: /home/davido/projects/protobuf/BUILD:604:1: Building libprotobuf_java.jar (78 source files, 1 source jar) failed (Exit 1)
java/core/src/main/java/com/google/protobuf/UnsafeUtil.java:44: error: package sun.misc does not exist
  private static final sun.misc.Unsafe UNSAFE = getUnsafe();
                               ^
java/core/src/main/java/com/google/protobuf/UnsafeUtil.java:290: error: package sun.misc does not exist
  private static sun.misc.Unsafe getUnsafe() {
                         ^
java/core/src/main/java/com/google/protobuf/UnsafeUtil.java:427: error: package sun.misc does not exist
    sun.misc.Unsafe unsafe;
            ^
java/core/src/main/java/com/google/protobuf/UnsafeUtil.java:429: error: package sun.misc does not exist
    MemoryAccessor(sun.misc.Unsafe unsafe) {
                           ^
java/core/src/main/java/com/google/protobuf/UnsafeUtil.java:506: error: package sun.misc does not exist
    JvmMemoryAccessor(sun.misc.Unsafe unsafe) {
                              ^
java/core/src/main/java/com/google/protobuf/UnsafeUtil.java:291: error: package sun.misc does not exist
    sun.misc.Unsafe unsafe = null;
            ^
java/core/src/main/java/com/google/protobuf/UnsafeUtil.java:295: error: package sun.misc does not exist
              new PrivilegedExceptionAction<sun.misc.Unsafe>() {
                                                    ^
java/core/src/main/java/com/google/protobuf/UnsafeUtil.java:297: error: package sun.misc does not exist
                public sun.misc.Unsafe run() throws Exception {
                               ^
java/core/src/main/java/com/google/protobuf/UnsafeUtil.java:298: error: package sun.misc does not exist
                  Class<sun.misc.Unsafe> k = sun.misc.Unsafe.class;
                                ^
java/core/src/main/java/com/google/protobuf/UnsafeUtil.java:298: error: package sun.misc does not exist
                  Class<sun.misc.Unsafe> k = sun.misc.Unsafe.class;
                                                     ^
Target //:protobuf_java failed to build
Use --verbose_failures to see the command lines of failed build steps.
INFO: Elapsed time: 68.809s, Critical Path: 19.64s