[MLton] debugging (was: experimental release)

[Matthew Fluet]

> I've been reading how the stabs debug format works at:
> http://sources.redhat.com/gdb/download/onlinedocs/stabs_toc.html
>
> ... and it sounds ... sane!
>
> In fact, after reading the documentation, I think it is quite
> feasible to make gdb work with mlton generated binaries.
> ... by work I also mean that it can read values.
> ... there might be problems with the MLton stack, though.

Oh, there was never an issue with emitting .stabs data, its rather that we 
don't have any reasonable data to emit.  We don't carry source variable 
location beyond type-checking, and it isn't clear how to carry such info 
though all the optimization passes.