Swap out some libc type aliases with std::ffi equivalents

Unfortunately std::ffi::c_size_t is currently experimental, and if I
define c_size_t = usize myself then cbindgen doesn't recognise it
properly and makes c_size_t a typedef of uintptr_t instead of just
replacing it with size_t.

ffi/src/constants.rs

@@ -1,4 +1,4 @@
-use libc::c_int;
+use std::ffi::c_int;
 
 #[no_mangle]
 pub static LCI_OK: c_int = 0;

ffi/src/helpers.rs

@@ -1,8 +1,8 @@
-use std::ffi::{CStr, CString};
+use std::ffi::{c_char, c_int, CStr, CString};
 use std::path::PathBuf;
 use std::slice;
 
-use libc::{c_char, c_int, size_t};
+use libc::size_t;
 use loot_condition_interpreter::{Error, GameType};
 
 use super::ERROR_MESSAGE;

ffi/src/lib.rs

@@ -6,12 +6,11 @@ mod helpers;
 mod state;
 
 use std::cell::RefCell;
-use std::ffi::CString;
+use std::ffi::{c_char, c_int, CString};
 use std::panic::catch_unwind;
 use std::ptr;
 use std::str::FromStr;
 
-use libc::{c_char, c_int};
 use loot_condition_interpreter::*;
 
 pub use constants::*;

ffi/src/state.rs

@@ -1,8 +1,9 @@
+use std::ffi::{c_char, c_int};
 use std::panic::catch_unwind;
 use std::path::PathBuf;
 use std::sync::RwLock;
 
-use libc::{c_char, c_int, size_t};
+use libc::size_t;
 use loot_condition_interpreter::State;
 
 use crate::constants::*;