Handle AddrSpace casts

[artemdinaburg]

We will eventually have to handle address space casts to support things like __thread and various memory specifications for embedded platforms. How to properly handle these is very machine context dependent and will need some kind of target-platform based configuration.

[surovic]

Potential solution : __attribute__((address_space(N)))

[artemdinaburg]

I really like the attribute solution; it should work well enough for most cases and is much better than just ignoring the addrspace change.