Also, even with configure --disable-largefile, I find that pg_config.h
still contains
/* Define to 1 to make fseeko visible on some hosts. */
#define _LARGEFILE_SOURCE 1
/* Define to 1 if fseeko (and presumably ftello) exists and is declared. */
#define HAVE_FSEEKO 1
This strikes me as probably Not a Good Thing, although I haven't dug to
see what the implications are.
regards, tom lane