javadoc: Include the default jvm options

This is necessary if you're on a host that must use JVM options to
configure successful network access (proxies, internal CAs, etc).

Until Change I3d810fcdf this wasn't necessary because the host JVM (and
the relevant bazel options) were used.

Change-Id: I019e58fe94bbd9e129a397dac16b6df79a519b74
Release-Notes: skip

tools/bzl/javadoc.bzl

diff --git a/tools/bzl/javadoc.bzl b/tools/bzl/javadoc.bzl
index 3add025..abf3b7a 100644
--- a/tools/bzl/javadoc.bzl
+++ b/tools/bzl/javadoc.bzl
@@ -37,6 +37,7 @@
         "mkdir %s" % dir,
         " ".join([
             "%s/bin/javadoc" % ctx.attr._jdk[java_common.JavaRuntimeInfo].java_home,
+            " ".join(["-J%s" % opt for opt in ctx.fragments.java.default_jvm_opts]),
             "-Xdoclint:-missing",
             "-protected",
             "-encoding UTF-8",
@@ -75,4 +76,5 @@
     },
     outputs = {"zip": "%{name}.zip"},
     implementation = _impl,
+    fragments = ["java"],
 )