Don't add Jack dependencies when building without Jack

Runtests add dependencies on the core library classes.jack files,
which don't exist when compiling with javac.  Disable the dependencies
when building without Jack for now.

Bug: 36902714
Test: m -j ANDROID_COMPILE_WITH_JACK=false tests
Change-Id: I40925c8c8536cc048e7308e6202db420154a18aa
(cherry picked from commit b6f707cb)