Self-compile and mlton.cm

[Matthew Fluet]

That fix to backend.fun eliminated my error.  I just finished a full
self-compile and will let it run through the regression tests and
benchmarks.  Assuming that all goes without problems, I'll send out the
new version of the x86-backend this afternoon.  Steve, would it easier for
you if I sent a tar.gz like in the source rpm (i.e., the whole directory
structure) or a tar.gz of the backend/x86-codegen directory and the other
files that I changed?  The second option hopefully wouldn't conflict with
any of your recent changes.