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)

tests/config_log.rs

@@ -3,12 +3,11 @@
 
 #[macro_use]
 extern crate lazy_static;
-extern crate libc;
 extern crate rusqlite;
 
 #[cfg(feature = "trace")]
 fn main() {
-    use libc::c_int;
+    use std::os::raw::c_int;
     use std::sync::Mutex;
 
     lazy_static! {