message: Add prefetchw to docs
diff: @@ -5096,6 +5096,13 @@ pointer types.
  void prefetch_{l1,l2,l3,nt}(void * uniform ptr)
  void prefetch_{l1,l2,l3,nt}(void * varying ptr)
  +The standard library also has routines to prefetch to the L1, L2, and L3
  +caches in anticipation of a write:
  +
  +::
  +
  + void prefetchw_{l1,l2,l3}(void * uniform ptr)
  + void prefetchw_{l1,l2,l3}(void * varying ptr)
  System Information
  ------------------
  