USEC_PER_SEC is defined by system headers on macOS, resulting in
a warning that it is redefined in time.h. Define it conditionally.
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
#define NSEC_PER_SEC 1000000000ULL
#define NSEC_PER_MSEC 1000000ULL
#define NSEC_PER_USEC 1000ULL
#define NSEC_PER_SEC 1000000000ULL
#define NSEC_PER_MSEC 1000000ULL
#define NSEC_PER_USEC 1000ULL
#define USEC_PER_SEC 1000000ULL
#define USEC_PER_SEC 1000000ULL
#define USEC_PER_MSEC 1000ULL
#define SEC_PER_MINUTE 60ULL
#define USEC_PER_MSEC 1000ULL
#define SEC_PER_MINUTE 60ULL