Factor out type size and alignment code from C ABI implementations

[sanxiyn]

[emberian]

Still relevant

[pcwalton]

Triage bump

[huonw]

Triage, still relevant. (Assuming this is about rustc::middle::trans::{cabi_arm, cabi_x86}, etc.)

[steveklabnik]

Triage bump: not totally clear to me.

[sanxiyn]

What is proposed here is to remove code duplications from rustc_trans::trans::cabi_*. Those modules define ty_size and ty_align functions, which are mostly but not exactly same as each other.

[steveklabnik]

Triage: all of those files are still there. I am unsure if they are de-duplicated enough to satisfy this ticket.