rPackages.opencv: fix build

pkgs/development/r-modules/default.nix

@@ -382,6 +382,7 @@ let
     nloptr = with pkgs; [ nlopt pkg-config ];
     n1qn1 = [ pkgs.gfortran ];
     odbc = [ pkgs.unixODBC ];
+    opencv = [ pkgs.pkg-config ];
     pak = [ pkgs.curl.dev ];
     pander = with pkgs; [ pandoc which ];
     pbdMPI = [ pkgs.mpi ];
@@ -1410,6 +1411,13 @@ let
       RGL_USE_NULL = "true";
     });
 
+
+    opencv = let
+      opencvGtk = pkgs.opencv.override (old : { enableGtk2 = true; });
+    in old.opencv.overrideAttrs (attrs: {
+      buildInputs = attrs.buildInputs ++ [ opencvGtk ];
+    });
+
     Rhdf5lib = let
       hdf5 = pkgs.hdf5_1_10.overrideAttrs (attrs: {configureFlags = attrs.configureFlags ++ ["--enable-cxx"];});
     in old.Rhdf5lib.overrideAttrs (attrs: {