Fix forward-decl of Bindings as "class", match definition.
Fix forward-decl of Bindings as "class", match definition.

(appease clang -Wmismatched-tags warning)

peti/nix,NixOS/nix,layus/nix,dtzWill/nix,layus/nix,ehmry/nix,dtzWill/nix,pikajude/nix,rycee/nix,ehmry/nix,peti/nix,dezgeg/nix,dtzWill/nix,rycee/nix,zimbatm/nix,shlevy/nix,rycee/nix,shlevy/nix,zimbatm/nix,zimbatm/nix,layus/nix,vcunat/nix,dezgeg/nix,ehmry/nix,shlevy/nix,shlevy/nix,pikajude/nix,dezgeg/nix,NixOS/nix,NixOS/nix,layus/nix,vcunat/nix,ehmry/nix,pikajude/nix,peti/nix,zimbatm/nix,dtzWill/nix,dtzWill/nix,dezgeg/nix,layus/nix,rycee/nix,ehmry/nix,NixOS/nix,vcunat/nix,dezgeg/nix,shlevy/nix,peti/nix,NixOS/nix,rycee/nix,peti/nix,vcunat/nix,ehmry/nix