message: add test for offseting fn ptr
diff: +fn f() -> i32 { 42 }
  +
  fn main() {
  let v = [1i16, 2];
  let x = &v as *const i16;
  let x = unsafe { x.offset(1) };
  assert_eq!(unsafe { *x }, 2);
  +
  + // fn ptr offset
  + unsafe {
  + let p = f as fn() -> i32 as usize;
  + let x = (p as *mut u32).offset(0) as usize;
  + let f: fn() -> i32 = std::mem::transmute(x);
  + assert_eq!(f(), 42);
  + }
  }
  