bug#47428: Problems building the up-to-date "devel" manual for the website

[Leo Famulari]

I noticed that the "devel" version of the online manual, which is
supposed to stay up to date, has not been updated since March 16, 2021:

https://guix.gnu.org/manual/devel/en/

There were some problems related to the recent guile-lib update, which
broke the build scripts in 'doc/build.scm', but that should be fixed
now.

I tried building it with `guix build -f doc/build.scm`, and it crashed
with a segmentation fault while building guix-translated-texinfo.drv,
with this message:

"mmap(PROT_NONE) failed"

I tried again, with --max-jobs=1, and it succeeded. So, maybe we just
need to update and reconfigure ci.guix.gnu.org, and try again.

Here is what I am working with:

------
$ guix describe
Generation 10   Mar 26 2021 20:11:33    (current)
  guix e8337f1
    repository URL: https://git.savannah.gnu.org/git/guix.git
    commit: e8337f1e45b57035c6e5d45133aa9412d4e5e882
------

And, I'm building 'doc/build.scm' from that same commit.