monit: fix build with libxcrypt

pkgs/tools/system/monit/default.nix

···
 , bison
 , flex
 , zlib
+, libxcrypt
 , usePAM ? stdenv.hostPlatform.isLinux
 , pam
 , useSSL ? true
···
   };
 
   nativeBuildInputs = [ bison flex ];
-  buildInputs = [ zlib.dev ] ++
+  buildInputs = [ zlib.dev libxcrypt ] ++
     lib.optionals useSSL [ openssl ] ++
     lib.optionals usePAM [ pam ];