libffi libnettle transitions request

[Dimitri John Ledkov]

To enable control flow protection (Intel CET) we need to kick of ABI
transition for libffi and libnettle, because trampolines / shadow
stack changes there change abi along with other changes that happened.

libffi transition means rebuild of ruby python php haskell
llvm-toolchains guile....

I guess we should have opened with libffi transition, but oh well.

Is it ok to proceed with libffi transition? It will be disruptive, due
to rebuilds triggering autopkgtests of all languages with bindings
effectively.

-- 
Regards,

Dimitri.