Yeah, I knew it was a missing font thing, but dang, there are a lot of moving parts.
First, make sure that the gsfonts package is installed (here's the FYI about it: https://www.freshports.org/print/gsfonts/)
$ sudo pkg install gsfontsYou can't tell it, but the original problem in lilypond was that it was trying to find (at least) one of these fonts (source: lilypond's configure script):
c059013l.pfb
c059016l.pfb
c059033l.pfb
c059036l.pfbconfigure says that fc-list should be able to see those fonts. Problem is that even after you install gsfonts, fc-list cannot see those (4) fonts.
$ fc-list | grep -E 'c0590(13|16|33|36)l\.pfb'
$ gsfonts puts them here on my system (FreeBSD 11.2): /usr/local/share/ghostscript/fonts
However, that's not a directory that fontconfig utils (via the various fontconfig config files) look at (including fc-cache). But, I knew that /usr/local/share/fonts was a font directory -- that's where all the other fonts go (that you install via packages).
So, rather than mess with the fontconfig config files (and take time to read about them), I did the "cheap" thing and symlinked the ghostscript fonts into /usr/local/share/fonts:
$ sudo ln -s /usr/local/share/ghostscript/fonts /usr/local/share/fonts/ghostscript(Sue me.)
Then, run
$ sudo fc-cacheYou should see that fc-list now sees those fonts (that lilypond needs).
$ fc-list | grep -E 'c0590(13|16|33|36)l\.pfb'
/usr/local/share/fonts/ghostscript/c059033l.pfb: Century Schoolbook L:style=Italic
/usr/local/share/fonts/ghostscript/c059013l.pfb: Century Schoolbook L:style=Roman
/usr/local/share/fonts/ghostscript/c059036l.pfb: Century Schoolbook L:style=Bold Italic
/usr/local/share/fonts/ghostscript/c059016l.pfb: Century Schoolbook L:style=Bold
$ Now, go back and generate your score (with lyrics) with lilypond. You should now see lyrics rendered.