[MLton] x86_64 port status

[Stephen Weeks]

> > What do you think of my suggestion of automatically defining PRIxPTR
> > in c-types.h?
> 
> That's reasonable, although I think it is equally reasonable to use 
> platform/<os>.h.  The auto-generation is convenient, but I think that it 
> will very soon quiesce, and we should be interested in situations where 
> the auto-generated sizes don't equal the sizes we've seen on other 
> instances of that platform.  In other words, do you really think it 
> reasonable to expect sparc-solaris to work unmodified on 32-bit sparcs and 
> 64-bit sparcs?

No.  My thought was that the reasoning for conditionally defining
PRIxPTR correctly is independent of OS, could be shared across all
platforms, and that the information is available in gen-types.c.  How
would you like the #if to look in platform/solaris.h to handle the two
possibilities (32-bit or 64-bit)?