Previously activate_latent_in() iterations looked like

for(export names in lib1) // hash table iteration
{
  for(symbol names in lib2) // list iteration
  {
    if(names equal && libsym->latent)
    {
      proc_activate_latent_symbol(proc, libsym)
    }
  }
}

This is inefficient both due to the double iteration but also since iterating
over a hash table in slow (have to look through all cells, even empty ones).
This patch turns this logic into

for(symbol names in lib2) // list iteration
{
  if(name in lib1 export names && libsym->latent) // hash table lookup
  {
    proc_activate_latent_symbol(proc, libsym)
  }
}

So there's no more double iteration, and the hash iteration was turned into a
hash lookup. Much better.