Add EV_DISPATCH and EV_RECEIPT EventFlag items for OpenBSD.
Add EV_DISPATCH and EV_RECEIPT EventFlag items for OpenBSD.

geofft/nix-rust,asomers/nix,carllerche/nix-rust,carllerche/nix-rust,geofft/nix-rust,nix-rust/nix,carllerche/nix-rust,geofft/nix-rust,nix-rust/nix,asomers/nix