In blf_glyph.cc there is a call to blf_glyph_ensure_icon which is wrapped in #ifndef WITH_HEADLESS.
So when WITH_HEADLESS is enabled, the function is defined in the header and called but is not compiled, which leaves it to fail in linking.
Could you turn this into a bugreport (or even better: a PR with the fix 
)? Here on the forum it will probably get lost.
I don’t currently have access to projects, which is why I mentioned it here.
ok, I’ll see if I can reproduce the error and create a bugreport.
I can’t reproduce it. For me if I enable WITH_HEADLESS it builds (and links) fine.
(linux ninja, tested both debug and release builds)
Maybe try a clean rebuild?
The issue was fixed in commit 779c432a291b796672e7c56659432f33ed5fee5f, but only in main.
Ideally this would have been backported to 5.0.1.