Ah, I nm'd all files in src/interfaces/libpq and got no hits for abort.
But I did get one in libpgport_shlib.a:
path_shlib.o:
U abort
0000000000000320 T canonicalize_path
0000000000000197 T cleanup_path
00000000000009e3 t dir_strcmp
...
--
Álvaro Herrera Valdivia, Chile
"People get annoyed when you try to debug them." (Larry Wall)