Build error with Android.mk

Integrating and building F-Droid in an AOSP-based ROM fails with this error:

> Compiling script into cache
Import includes file: /home/fabi/android/omni/out/target/product/bullhead/obj/SHARED_LIBRARIES/libnfc_nci_jni_intermediates/import_includes

FAILURE: Build failed with an exception.

* What went wrong:
Could not open buildscript class cache for settings file '/home/fabi/android/omni/packages/apps/F-Droid/settings.gradle' (/home/fabi/.gradle/caches/2.5/scripts/settings_11n3g8sqllmy6gm19hqb899bm/SettingsScript/buildscript).
> groovyjarjarantlr/TokenStreamRecognitionException : Unsupported major.minor version 52.0

* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output.

BUILD FAILED

This error happens only with F-Droid. I'm building with latest master and using openjdk 1.7. Is !244 trying to fix this? Until now it does not. @spudowiar