How do we flag a feature as implemented for GNU Guile cond-expand in Guix packages?

[Yuval Langer]

Hi,

I have packaged several SRFI example implementations now and it had
occurred to me that I did not flag any of them as implemented for the
cond-expand macro.

I have guile-srfi-235 installed but just this moment I've tested in
the GNU Guile REPL:

    (cond-expand (srfi-235 'supported) (else 'not-supported))

But its value is the not-supported symbol.

Reading the manual I see:

> Other SRFI feature symbols are defined once their code has been loaded with 
> ‘use-modules’, since only then are their bindings available.

But when I run this script:

    (use-modules (srfi srfi-235))

    (display
     (cond-expand
      (srfi-235 'srfi-235-supported)
      (else 'srfi-235-not-supported)))

    (newline)

The line "srfi-235-not-supported" is printed.

Is there a way of adding cond-expand features to GNU Guile, maybe in
the Guix package definitions?

Many thanks,
Yuval Langer.