Cannot move to a newer Rust version

[lasiotus]

rust-lang/cc-rs#1225 changed target parsing to a static pregenerated list of "targets known to rustc". As Motor OS is not known to rustc, building x86_64-unknown-moturus fails with newer Rust dist.

[lasiotus]

Discussion in cc-rs: rust-lang/cc-rs#1317

[lasiotus]

Added rust-lang/rust#134344 to bump cc version.

[lasiotus]

This is more or less fixed.