NIFC cannot handle stat

[Araq]

NIFC wraps every array in its own struct so that we get the correct copy semantics from C. This is generally a good idea but fails for code like:

type
  Dirent* {.importc: "struct dirent", header: "<dirent.h>".} = object
    d_type* {.importc: "d_type".}: uint8
    d_name* {.importc: "d_name".}: array[DirNameLen, char]

The array d_name is not under NIFC's control and has no such struct wrapper. NIFC needs to special case the access obj.d_name in the AtC case:

# genexprs.nim
  ...
  of AtC:
    let (a, i) = sons2(t, n)
    genx c, t, a
    c.add Dot
    c.add "a"
    c.add BracketLe
    genx c, t, i
    c.add BracketRi