[MLton] Real.toString broken on 64 bit

[Wesley W. Terpstra]

This works fine on 32 bit, but:
> terpstra at tokyo:~$ ldd bug
> 	libm.so.6 => /lib64/libm.so.6 (0x00002b88fd0d0000)
> 	libgmp.so.3 => /lib64/libgmp.so.3 (0x00002b88fd252000)
> 	libc.so.6 => /lib64/libc.so.6 (0x00002b88fd391000)
> 	/lib64/ld-linux-x86-64.so.2 (0x00002b88fcfb8000)
> terpstra at tokyo:~$ ./bug
> Not 1: 2.68403211433E~112
> terpstra at tokyo:~$ cat bug.sml
> val () = print ("Not 1: " ^ Real.toString 1.0 ^ "\n")

This is with svn/HEAD. I am not sure if it matters, but the default  
user space is 32 bit, but with 64 bit libraries in /lib64. The MLton  
used is a 32->64 bit cross compiler.