PySSL_RAND_atfork_child(void) can be simplified by calling
_PyTime_gettimeofday(). This function uses the most(*) accurate
function and already implements fallbacks on error.

(*) _PyTime_gettimeofday() does not use clock_gettime() because of a
linker issue: Python is not linked to librt, which is required to get
clock_gettime() on Linux with glibc < 2.17. So you get a few less bits
of entropy, but does it really matter? If it matters, you have
probably to use a better random of entropy than the system time...

Anyway, it would be easier to move the _PyTime_timeval and similar
structures into the seed structure instead of shifting bits.