And more, can't I build Guile once, into some other directory and rather
than rebuilding it each time place a symlink into the LilyPond
installation directory? This would be very useful as I tend to have
multiple builds in parallel.
Multiple builds of lilypond at the same time?
Yes, definitely. I often (at least in times when I'm actually working on
stuff in LilyPond) have multiple builds side-by-side. For example one
from current master and others from different open branches or even from
earlier releases. Actually Frescobaldi even has got explicit support for
this upon Janek's request.