Ctrl-C'ing yields the same output as before, plus a success message:
*** Successfully generated feta20.pfb! ***
(The file feta20.pfb does indeed exist, and can be viewed in the
build/mf/out, in a temporary folder. It contains all the glyphs included in
feta20.mf, no more, no less. So, no noteheads or flags, etc. The glyphs are
not assigned Unicode codepoints, but that's not surprising. This subfont is
supposed to be temporary and would ordinarily be merged with the other
subfonts with gen-emmentaler-fontforge.py, after which they would receive
Unicode values.)
I also ran make on current master with VERBOSE=1, and got the same stuff as
2.18.0 *before* the copyright notice, but none of 2.18.0's stuff *after* it.
At any rate, that *probably* pins down Fontforge as the source of the
issues. It's odd, though--an update couldn't have introduced the bug, since
a version newer than 2017 isn't available on LilyDev's apt repository. And
the bug couldn't have just been there all along, since it's worked
perfectly for me for over a month.
I'd really like to see if someone can reproduce any of this on a different
machine and a fresh LilyDev VM, so please holler if you're willing to try!