newlib: stop making .def generation conditional

newlib: stop making .def generation conditional

Generating these files is very cheap, so let's just do it all the time.
This makes the build logic simpler, and keeps errors for slipping in in
codepaths that are not well tested.  Creating these files doesn't mean
they'll be included in the manual implicitly.

For example, some of the nano stdio files break documentation because
they don't have any chew directives in them.  But no one noticed since
that code path is rarely enabled.  So drop the _i and _float def files.