posixtm-tests: port to buggy compiler

posixtm-tests: port to buggy compiler

Problem reported by Simon Josefsson in
<http://lists.gnu.org/archive/html/bug-gnulib/2012-06/msg00246.html>.
* modules/posixtm-tests (Depends-on): Add stdint.
* tests/test-posixtm.c (struct posixtm_test.t_expected):
Now of type int_least64_t, not int64_t, both because that's
what INT64_C returns and because int_least64_t works even
on 72-bit hosts.
(T): Use INT64_C on constants outside the traditional int range,
to work around compiler bug noted by Simon.