SSA backend update

[Stephen Weeks]

I've made some progress.  I am now able to compile all the regressions and
benchmarks using the SSA backend with the C code generator.  I tried a self
compile, which is able to generate the C (somewhat slowly), but which gcc is
unable to compile.  Here's a snippet of the log.

   Compile SML finished in 198.07 + 151.86 (43% GC)
...
   Compile C starting
      gcc -S -DNODEBUG -DMLton_safe=TRUE -DMLton_detectOverflow=TRUE \
          -I/home/sweeks/mlton/include -O1 -w -fomit-frame-pointer \
          -fno-strength-reduce -m486 -malign-loops=2 -malign-jumps=2 \
          -malign-functions=2 -o /tmp/fileUT8VId.s /tmp/file0B2HEr.c
gcc: Internal error: Killed (program cpp0)
Please submit a full bug report.
See <URL:http://bugzilla.redhat.com/bugzilla/> for instructions.


I'm inclined to ignore this problem, and move on to debugging the SSA backend
with the native codegen, for which there are still many regression failures.
Matthew, I'm probably gonna need some help here in understanding what native
codegen invariants I'm violating, and how to get maximal debugging info and
asserts on in the native codegen.