[Fortran] check the length of internal file

With the following example, gfortran has runtime error:

```
program main
character(len=5) :: s
write(s, '(3I0)') [11, 22, 33]
print '(a)', s
end program main
```

since the written string is longer than string `s`.

It would be nice to have a check that will determine such situations (especially when runtime values are used).