aws-lc-sys build should check for minimal bindgen version

[elmarco]

During the build of a project that depends on rustls, and includes aws-lc-sys:

bindgen-STDERR: error: invalid value '1.59' for '--rust-target <RUST_TARGET>': Got an invalid rust target. Accepted values are of the form "1.0" or "nightly".

I used to have bindgen 0.65.1 installed.
After upgrading to 0.69.4, issue disappeared.

[justsmth]

Hello! Thanks for reporting this.

I put up a PR to help improve our handling of this: #494

[justsmth]

This is resolved with the release of aws-lc-rs v1.9.0.