Try to fix portability bugs in recent pgbench commits.

Try to fix portability bugs in recent pgbench commits.

1.  pg_time_usec_t needs to be printed with INT64_FORMAT, not %ld, or 32
bit systems complain, per lapwing.

2.  Some Windows compilers didn't like a thread function not marked with
__stdcall, per whelk; let's see if this fixes the problem.