Require FFI option. Punt compile-/run-time separation.

Require FFI option.  Punt compile-/run-time separation.

This eliminates unanalyzable (unCREFable) syntax transformers, and
compile-time imports.

Bind c-includes in (gtk) so that it does not need to be c-included in
every subpackage.  This assumes compile-system is used, and that
gtk.scm/bin/com is loaded before subpackages are compiled.