Fix build on arm64 linux.

On arm64 linux, c_char is u8. CStr::from_ptr is documented to take an
i8, but this is not accurate (see
rust-lang/rust#113735); instead, it takes
c_char, which is sometimes but not always the same. One time it is
different is on aarch64 Linux, so without this commit, cubeb-rs fails to
build there.

cubeb-sys/src/device.rs

@@ -182,7 +182,7 @@ impl Default for cubeb_device_info {
 
 impl fmt::Debug for cubeb_device_info {
  fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
- fn optional_c_str(c_str: *const i8) -> Option<*const i8> {
+ fn optional_c_str(c_str: *const c_char) -> Option<*const c_char> {
  (unsafe { c_str.as_ref() }).map(ptr::from_ref)
  }
  f.debug_struct("cubeb_device_info")