gen: Add saw_union field to GenCtx
gen: Add saw_union field to GenCtx

catdesk/rust-bindgen,emilio/rust-bindgen,rust-lang/rust-bindgen,jdub/rust-bindgen,catdesk/rust-bindgen,emilio/rust-bindgen,jdub/rust-bindgen,rust-lang/rust-bindgen,jdub/rust-bindgen,catdesk/rust-bindgen,jdub/rust-bindgen,emilio/rust-bindgen,rust-lang/rust-bindgen,emilio/rust-bindgen,catdesk/rust-bindgen,rust-lang/rust-bindgen,emilio/rust-bindgen