Defined in Vim as such:

```c
init_mappings()
{
#if defined(MSDOS) || defined(MSWIN) || defined(OS2) || defined(MACOS)
    int       i;

    for (i = 0; i < sizeof(initmappings) / sizeof(struct initmap); ++i)
       add_map(initmappings[i].arg, initmappings[i].mode);
#endif
}
```

Why would unix not need this, or why did Windows and Mac need it?