RTS claims to bundle libffi even when it doesn't

The rts.cabal file added by 5dea62fb claims unconditionally that the rts library will "bundle" libCffi (using the extra-bundled-libraries declaration). Unfortunately it's quite hard to know precisely what "bundle" means in this context since no comment was added. However, I can't think of any reasonable interpretation of the word where this claim is true. Afterall, on x86-64 the RTS doesn't even depend upon libffi.

My suspicion is that this was intended to only capture the case where we are (1) using libffi for adjustors, and (2) aren't using the system libffi. However, it would be good to get confirmation from @angerman.