haskellPackages.Agda: set mainProgram (#425829)

pkgs/build-support/agda/default.nix

@@ -65,10 +65,10 @@ let
       }
       ''
         mkdir -p $out/bin
-        makeWrapper ${lib.getBin Agda}/bin/agda $out/bin/agda \
+        makeWrapper ${lib.getExe Agda} $out/bin/agda \
           ${lib.optionalString (ghc != null) ''--add-flags "--with-compiler=${ghc}/bin/ghc"''} \
           --add-flags "--library-file=${library-file}"
-        ln -s ${lib.getBin Agda}/bin/agda-mode $out/bin/agda-mode
+        ln -s ${lib.getExe' Agda "agda-mode"} $out/bin/agda-mode
       '';
 
   withPackages = arg: if isAttrs arg then withPackages' arg else withPackages' { pkgs = arg; };

pkgs/development/haskell-modules/configuration-nix.nix

@@ -1362,6 +1362,8 @@ builtins.intersectAttrs super {
     # very useful.
     # Flag added in Agda 2.6.4.1, was always enabled before
     (enableCabalFlag "debug")
+    # Set the main program
+    (overrideCabal { mainProgram = "agda"; })
     # Split outputs to reduce closure size
     enableSeparateBinOutput
   ];