Missing <stdio.h> functions

The following appear to be missing from `<stdio.h>`:
- `freopen`
- `ungetc` (probably as a user defined weak function if it doesn't make sense in fileioc)
- `setbuf`
- `setvbuf`
- `fgetpos`
- `fsetpos`
- `fpos_t`
- `tmpnam`
- `tmpfile`
