Description of the problem from Matthieu Dorier:

darshan-ruby does an #include <darshan-logutil.h>, which itself does a #include <darshan-log-format.h> which itself contains

#ifndef DARSHAN_CONFIG_H
    #error Must define DARSHAN_CONFIG_H
#endif

#include DARSHAN_CONFIG_H

so within my C file I also have to add the following line before including darshan-logutil.h:
#define DARSHAN_CONFIG_H "darshan-util-config.h"

The logutil.h header is relying on autoconf for HAVE_INTTYPES_H and PRI macros. The PRI logic can be moved to another header (it isn't directly used in logutil.h), and we can then switch to the more portable stdint header for fixed-size integer definitions.