[MLton] x86_64 port status

[Florian Weimer]

* Matthew Fluet:

> I'm surprised this isn't defined, as it should be in <stdint.h>.

<stdint.h> is not very widely available (as far as historic platforms
are concerned).  Use <sys/types.h> or <inttypes.h>.  Here's what the
autoconf manual has to say about the topic:

`inttypes.h' vs. `stdint.h'
     Paul Eggert notes that: ISO C 1999 says that `inttypes.h' includes
     `stdint.h', so there's no need to include `stdint.h' separately in
     a standard environment.  Many implementations have `inttypes.h'
     but not `stdint.h' (e.g., Solaris 7), but I don't know of any
     implementation that has `stdint.h' but not `inttypes.h'.  Nor do I
     know of any free software that includes `stdint.h'; `stdint.h'
     seems to be a creation of the committee.