x86 update

[Matthew Fluet]

> I integrated it and ran some tests over the weekend.  The self compile failed
> during the x86 code gen pass due to running out of memory.  Something really bad 
> must have happened, since the max live with the old x86-codegen was about 60M.
> I had made some changes to the closure converter, but I can't imagine how they
> would have caused this.  Anyways, I'll revert back to the old x86-codegen and
> see if I can do a self-compile there.

Very odd.  I haven't had any issues with memory on my recent self-compiles
(including a few yesterday).  Memory usage in the x86-codegen should be
proportional to the size of the chunks and the size of the blocks; I would
guess those would be dictated more by backend.fun and chunkify.fun than by
the closure converter.

> Matthew, do you want a snapshot?

Sure.  If you encounter this some more, you might try changing the
  val tracer =
definitions at the top of x86-{translate,simplify,allocate-registers}.fun.
That will use the original traceCall which might pinpoint where the memory
explosion is occuring.