[ast-optimizer-branch] Merged PCH changes into branch

[Diego Novillo]

This latest merge brought in the PCH patches, which disrupted a
few things.  The branch adds a field to the tree structure which
gengtype wants to process.  But this results in a chain of
changes that are too annoying to deal with (we have to start
marking many structures in tree-*).

I have always wanted to get rid of this additional tree_node
field, so I just marked it 'skip'.  I also had to disable
simple-break-elim.c and simple-goto-elim.c because of the changes
to the hash table implementation.  Sebastian, could you look into
this?  If not, I'll just put it in my TODO.


Diego.