In fontname | Graphviz we read,
If Graphviz was built using the fontconfig library, the latter library will be used to search for the font.
(By the way, why “the latter”? There is no “former”.)
How do I know whether I have built Graphviz using fontconfig?
Update. I ran
./configure 2>&1 | grep -i fontconfig
and
make 2>&1 | grep -i fontconfig
and
sudo make install 2>&1 | grep -i fontconfig
and only the last pipeline outputs anything, which is
libtool: install: ((…) gcc (…) -lfontconfig (…))
Can this be a proof?