Fix build using nix-build on GHC-8.4.2

Fixes #116

Author: basvandijk

opencv-extra/Setup.hs

@@ -3,6 +3,6 @@ import System.Environment ( getArgs )
 
 main = do
     args <- getArgs
-    let args' | "configure" `elem` args = args ++ ["--with-gcc","c++", "--with-ld","c++"]
+    let args' | "configure" `elem` args = args ++ ["--with-gcc","c++"]
               | otherwise               = args
     defaultMainArgs args'

opencv/Setup.hs

@@ -3,6 +3,6 @@ import System.Environment ( getArgs )
 
 main = do
     args <- getArgs
-    let args' | "configure" `elem` args = args ++ ["--with-gcc","c++", "--with-ld","c++"]
+    let args' | "configure" `elem` args = args ++ ["--with-gcc","c++" ]
               | otherwise               = args
     defaultMainArgs args'

overlay.nix

@@ -30,6 +30,13 @@ let
         shellHook = ''
           export hardeningDisable=bindnow
         '';
+        # TODO: cabal2nix automatically adds:
+        #
+        #   configureFlags = ["--with-gcc=${stdenv.cc}/bin/c++" "--with-ld=${stdenv.cc}/bin/c++"];
+        #
+        # This is not needed anymore and will actually break the build.
+        # So lets remove this from cabal2nix or ask @peti to do it.
+        configureFlags = [];
       });
 
       opencv-examples =
@@ -77,6 +84,7 @@ let
           shellHook = ''
             export hardeningDisable=bindnow
           '';
+          configureFlags = [];
         });
 
       opencv-extra-examples =