POSIX specification:
https://pubs.opengroup.org/onlinepubs/9799919799/basedefs/sys_time.h.html
Portability problems fixed by Gnulib:
tv_sec type that is
narrower than time_t
on some native Windows platforms:
mingw64 in 64-bit mode,
mingw64 in 32-bit mode when __MINGW_USE_VC2005_COMPAT is defined,
MSVC 14 in 64-bit mode,
MSVC 14 in 32-bit mode when _USE_32BIT_TIME_T is not defined.
See Avoiding the year 2038 problem, for portability issues with
time_t and the time_t component of struct timeval.
Portability problems not fixed by Gnulib:
tv_sec type that is
wider than time_t:
OpenBSD 5.1 in 64-bit mode.