Bump clang-sys to 0.28.0
Bump clang-sys to 0.28.0

Signed-off-by: Robert-André Mauchin <aa2d2b4191fcc92df7813016d4b511c37a1b9a82@gmail.com>

emilio/rust-bindgen,emilio/rust-bindgen,emilio/rust-bindgen,emilio/rust-bindgen,rust-lang/rust-bindgen,emilio/rust-bindgen,rust-lang/rust-bindgen,rust-lang/rust-bindgen,rust-lang/rust-bindgen