ocamlPackages.curses: Fix build after ncurses5 changes
ocamlPackages.curses: Fix build after ncurses5 changes

Fixes build after commit 3d24ae9b4426bb8adfcb08de57be21fdf0a377f8:

https://github.com/NixOS/nixpkgs/commit/3d24ae9b4426bb8adfcb08de57be21fdf0a377f8#commitcomment-27714305

Thanks to dtzWill for the pointer:
https://github.com/NixOS/nixpkgs/pull/34477#issuecomment-367359351

NixOS/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,SymbiFlow/nixpkgs,SymbiFlow/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs,SymbiFlow/nixpkgs,SymbiFlow/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs,SymbiFlow/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs,SymbiFlow/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs