[FIX] Teach RegionGenerator to respect and update dominance

  When we generate code for a whole region we have to respect dominance
  and update it too.
  The first is achieved with multiple "BBMap"s. Each copied block in the
  region gets its own map. It is initialized only with values mapped in
  the immediate dominator block, if this block is in the region and was
  therefor already copied. This way no values defined in a block that
  doesn't dominate the current one will be used.
  To update dominance information we check if the immediate dominator of
  the original block we want to copy is in the region. If so we set the
  immediate dominator of the current block to the copy of the immediate
  dominator of the original block.

llvm-svn: 230774