Remove ugly libc_bitflags hack for mac/ios.
Remove ugly libc_bitflags hack for mac/ios.

xd009642/nix,nix-rust/nix,geofft/nix-rust,MarkusJais/nix-rust,carllerche/nix-rust,MarkusJais/nix-rust,MarkusJais/nix-rust,xd009642/nix,geofft/nix-rust,xd009642/nix,Susurrus/nix,nix-rust/nix,asomers/nix,geofft/nix-rust,Susurrus/nix,asomers/nix,carllerche/nix-rust,Susurrus/nix,carllerche/nix-rust