I did some more tests.

The value is:
(__extension__(9223372036854775807LL))

#define   LLONG_MAX       (__extension__(9223372036854775807LL))

and

#define   ULLONG_MAX      (__extension__(0xffffffffffffffffULL))

Maybe the paranthesis are causing this problem.

fiddlehead:~ $ cat test.c
#define XJCRX   (__extension__(9223372036854775807LL))

#if !XJCRX
#error here
#endif

fiddlehead:~ $ gcc -E test.c
test.c:3: syntax error
# 1 "test.c"


   Jeremy C. Reed
   http://bsd.reedmedia.net/