Check for the sys/cdefs.h header which on some systems defines the __warn_references macro.

config.h.in

@@ -65,6 +65,9 @@
 /* Define to 1 if you have the <syslog.h> header file. */
 #undef HAVE_SYSLOG_H
 
+/* Define to 1 if you have the <sys/cdefs.h> header file. */
+#undef HAVE_SYS_CDEFS_H
+
 /* Define to 1 if you have the <sys/param.h> header file. */
 #undef HAVE_SYS_PARAM_H
 

configure.in

@@ -15,7 +15,7 @@ AC_PROG_MAKE_SET
 AM_CONFIG_HEADER(config.h)
 AM_CONFIG_HEADER(json_config.h)
 AC_HEADER_STDC
-AC_CHECK_HEADERS(fcntl.h limits.h strings.h syslog.h unistd.h [sys/param.h] stdarg.h)
+AC_CHECK_HEADERS(fcntl.h limits.h strings.h syslog.h unistd.h [sys/cdefs.h] [sys/param.h] stdarg.h)
 AC_CHECK_HEADER(inttypes.h,[AC_DEFINE([JSON_C_HAVE_INTTYPES_H],[1],[Public define for json_inttypes.h])])
 
 # Checks for typedefs, structures, and compiler characteristics.