Android: Ignore some generated files

/obj/ is used by ndk debugging (gdb) in some scenarios.  I ended up adding `android:debuggable="true"` to `AndroidManifest.xml` and `<fileset dir="../../libs/armeabi-v7a" includes="gdbserver" />` to `custom_rules.xml` as  well as `APP_ABI := armeabi-v7a` to `Android.mk` to convince ndk-gdb to work, but I'm not sure which of those are necessary.

But in any case /Source/Android/libs/ ought to be ignored since that's where the built .so goes.

-[Unknown]