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/trace.rs

@@ -1,6 +1,6 @@
 //! Tracing and profiling functions. Error and warning log.
 
-use libc::{c_char, c_int, c_void};
+use std::os::raw::{c_char, c_int, c_void};
 use std::ffi::{CStr, CString};
 use std::mem;
 use std::ptr;