I have just completely re-synced and am not getting an error when trying to build for grouper.
It seems that something is trying to build koush's superuser for recovery. I've been poking around and and figure out how to get it to stop trying to build this. I see that some others had successful builds recently and I don't see any recent commits to nitro's repos that could cause this. I imagine it came from something synced from the CM repos. If anybody comes across a solutions please post it here.
make: *** No rule to make target `bootable/recovery/su/../../../external/koush/Superuser/Superuser/jni/su/su.c', needed by `/home/aaron_android/elementalx/out/target/product/grouper/obj/RECOVERY_EXECUTABLES/su_intermediates/../../../external/koush/Superuser/Superuser/jni/su/su.o'. Stop.