bug#35919: recutils package does not install emacs rec-mode

[Jack Hill]

I've looked at this some, and it looks to me like it is a change in the 
upstream build system. I can confirm that the problem arrived in Guix when 
the package version was updated from 1.7 to 1.8. In particular, it looks 
like lispdir is no longer being set by configure. The configure from 1.7 
has

```
  if test "x$lispdir" = x; then
    lispdir='${datarootdir}/emacs/site-lisp'

  fi
```

while the configure from 1.8 does not mention lispdir at all.

I'll ask the recutils upstream if this was intentional.

In the meantime, what do we want to do in Guix? I see two options: one is 
patching the build system, and the other is adding a phase to install the 
elisp files. The latter seems to me like the clearest and easiest 
approach here.

Thoughts?

Best,
Jack