This should be named "extrapatch-tokudb" to be more consistent with the rest of the tree.

I think these should be set using helpers and sooner in the Makefile, for example:

TOKUDB_CMAKE_ON=      -DUSE_CTAGS=0
TOKUDB_VARS=          ONLY_FOR_ARCH=amd64
ONLY_FOR_ARCH_REASON= TokuDB engine does not compile on ${ARCH}

The ONLY_FOR_ARCH_REASON can be set regardless as it's a no-op if ONLY_FOR_ARCH is not defined.

(while there, you could convert the two options blocs just before to helpers too.)

Thinking about it, this is a "server" only option, maybe you should add:

OPTIONS_EXCLUDE=TOKUDB

To databases/percona56-client/Makefile, so that it's not available as an option there.

That's not needed any more. (Sorry, should have said earlier.)