mmap fails when compiled for 32bit

https://users.suse.com/~aj/linux_lfs.html

```
#ifndef __USE_FILE_OFFSET64
extern void *mmap (void *__addr, size_t __len, int __prot,
int __flags, int __fd, __off_t __offset) __THROW;
#else
# ifdef __REDIRECT_NTH
extern void * __REDIRECT_NTH (mmap,
(void *__addr, size_t __len, int __prot,
int __flags, int __fd, __off64_t __offset),
mmap64);
# else
# define mmap mmap64
# endif
#endif
#ifdef __USE_LARGEFILE64
extern void *mmap64 (void *__addr, size_t __len, int __prot,
int __flags, int __fd, __off64_t __offset) __THROW;
#endif
```

on 32bit platforms, behind the scenes, the type of `off_t` changes depending on how a program is compiled
glibc then uses a macro to map `mmap` to either the real `mmap` or the `mmap64` version, based on the size of `off_t`

haskell base was compiled with large-file-support, so `COff` is 64bits, but then the ffi grabs the raw `mmap` symbol, the 32bit version

the simplest solution is to use cbits and `Word64` to get the values into c code, then (with LFS enabled), call mmap from c, and let the macro do its job