* stdint_.h (intmax_t) [defined intmax_t]: Do not declare.

* stdint_.h (intmax_t) [defined intmax_t]: Do not declare.
(uintmax_t) [defined uintmax_t]: Do not declare.
(SIZE_MAX) [defined SIZE_MAX]: Do not define.
This works around a problem if intmax_t.m4 and/or uintmax_t.m4
and/or size_max.m4 are also used.  Problem reported by Mark D. Baushke.
(SIZE_MAX): Define to ((size_t) -1), not (~(size_t)0), for the
sake of portability to weird hosts that C allows (though we don't
know of any practical examples).