Hmm. Using FreeType 2.12.1 (self-compiled) and FontConfig 2.13.1 (as
provided by my openSUSE box), running `lilypond --verbose` (from
current git) on the above input gives
```
...
[nonexistent_bold_3.8662109375]
Finding the ideal number of pages...
[lilypond_serif_3.8662109375]
CFF name for font C059-Roman is the same.
Fitting music on 1 page...
Drawing systems...
Initializing embedded CFF font list.
[/usr/share/fonts/truetype/arialbd.ttf]
Embedding CFF font `C059-Roman'.
[/home/wl/.fonts/urw-fonts/C059-Roman.otf]
...
```
as expected, and I see 'ABC' in the created output file.
I've also repeated the same with fontconfig 2.14.1 and I get identical
output.