I think it is a bad idea to run Guile on the docfiles while
suppressing the output as the first thing after it's built.

While developing for Guile it happens to me all the time that build
gets stuck at this place without any explanation.

What about running the test-suite at this point instead, and make sure
that also primary error messages (not relating to the tests) gets to
standard output so that one can see what is wrong?