message: Fix calloc test
  Forgot to free the memory. Miri found the bug :)
diff: @@ -17,10 +17,10 @@ fn main() {
  let p3 = libc::calloc(0, 20);
  assert!(p3.is_null());
  - let p4 = libc::calloc(4, 8) as *const u8;
  + let p4 = libc::calloc(4, 8);
  assert!(!p4.is_null());
  -
  - let slice = slice::from_raw_parts(p4, 4 * 8);
  + let slice = slice::from_raw_parts(p4 as *const u8, 4 * 8);
  assert_eq!(&slice, &[0_u8; 4 * 8]);
  + libc::free(p4);
  }
  }
  