Different bootclasspath for droiddoc.

- If it's host module, don't set bootclasspath;
- If it's arget module,
  - It can build against the API stubs;
  - It can build against a historical SDK version;
  - It can build against core.jar

Change-Id: Id1ec3ba624bc38068b206ad7173f4facf590e021
1 file changed