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/functions.rs

@@ -54,7 +54,7 @@ use std::ffi::CStr;
 use std::mem;
 use std::ptr;
 use std::slice;
-use libc::{c_int, c_char, c_void};
+use std::os::raw::{c_int, c_char, c_void};
 
 use ffi;
 use ffi::sqlite3_context;
@@ -508,7 +508,7 @@ mod test {
     extern crate regex;
 
     use std::collections::HashMap;
-    use libc::c_double;
+    use std::os::raw::c_double;
     use self::regex::Regex;
     use std::f64::EPSILON;