Add missing --rust-target flags on test case.
See
-// bindgen-flags: --default-enum-style rust_non_exhaustive --raw-line '#![cfg(feature = "nightly")]' --raw-line '#![feature(non_exhaustive)]'
+// bindgen-flags: --default-enum-style rust_non_exhaustive --rust-target nightly --raw-line '#![cfg(feature = "nightly")]' --raw-line '#![feature(non_exhaustive)]'
enum Planet {
earth,
