Improve compilation of Pancake's exception

[minhddo]

Pancake's Raise semantics has a check that the exception value shape is smaller than 32 words (see code below), because it is currently compiled into stores to wordLang Temp stores later on in the compiler. A possible improvement is to remove this check which can allow arbitrary shape exception and compile it in a different manner.

  (evaluate (Raise eid e,s) =
    case (FLOOKUP s.eshapes eid, eval s e) of
      | (SOME sh, SOME value) =>
         if shape_of value = sh ∧
            size_of_sh_with_ctxt s.structs (shape_of value) <= 32
         then (SOME (Exception eid value),empty_locals s)
         else (SOME Error,s)
     | _ => (SOME Error,s)) /\

[IlmariReissumies]

One easy compilation strategy suggested by @myreen during the recent Pancake meeting is to allocate a global variable for storing exception payloads that aren't 1-shaped, and put the payload there. This can then be compiled into exceptions that always use a 1 shape before pan_globals.