* get rid of the pointless fences
 * make seed_len 16 instead of 32, which is accurate since it was
   already padding the rest anyway; now we do 1 pad instead of 2.
 * secureZero to clear the AT_RANDOM auxval
 * add a flag root source files can use to disable the start code. This
   is in case people want to opt out of the initialization when they
   don't depend on it.