Build debug version of libroc when building debug AAR

[gavv]

We build two versions of AAR, debug and release, and both use release version of native libroc.so.

It would be convenient to build debug version of libroc, and use it in debug version of AAR. Debug version of libroc should have better stacktraces.

libroc is built using scripts/android/build_roc.sh. Currently it builds 4 versions of the lib (for 4 android ABIs). Now it'll need to build 8 versions (debug + release for each ABI), and gradle will need to use appropriate version.

To enable debugging, pass --enable-debug option to scons.