Remove the dependency on libc

Recent versions of bindgen use `std::os::raw` over `libc`, but currently
`libsqlite3-sys` is overriding that. `std::os::raw` is a subset of
`libc` that exports only the relevant type definitions, but not any
functions which require additional linking. This enables
`libsqlite3-sys` to be more easily used on targets that may not have a
libc available (presumably sqlite itself would have been compiled with
musl in that case)

src/error.rs

@@ -2,7 +2,7 @@ use std::error;
 use std::fmt;
 use std::path::PathBuf;
 use std::str;
-use libc::c_int;
+use std::os::raw::c_int;
 use {ffi, errmsg_to_string};
 use types::Type;