[RFC] Small include cleanup

Regarding 7b56ebc9ef65d2f3544c21bacb9d2103a58bdd91, see the following at http://pubs.opengroup.org/onlinepubs/009695399/basedefs/inttypes.h.html:
```
The <inttypes.h> header shall include the <stdint.h> header.
```

I initially thought this was for MSVC compatibility, but there are already a bunch more files that only include `inttypes.h`, so I'm not totally sure.