openctm: fix darwin support

pkgs/by-name/op/openctm/package.nix

@@ -6,6 +6,7 @@
   libglut,
   gtk2,
   libGLU,
+  darwin,
 }:
 
 stdenv.mkDerivation (finalAttrs: {
@@ -26,17 +27,29 @@ stdenv.mkDerivation (finalAttrs: {
 
   nativeBuildInputs = [ pkg-config ];
 
-  buildInputs = [
+  buildInputs =
+    [
       libglut
-    gtk2
       libGLU
-  ];
+    ]
+    ++ lib.optionals stdenv.hostPlatform.isLinux [ gtk2 ]
+    ++ lib.optionals stdenv.hostPlatform.isDarwin [ darwin.apple_sdk.frameworks.Cocoa ];
 
-  postPatch = ''
+  postPatch =
-    substituteInPlace tools/tinyxml/Makefile.linux \
+    lib.optionalString stdenv.hostPlatform.isLinux ''
+      substituteInPlace "tools/tinyxml/Makefile.linux" \
         --replace-warn "-Wno-format" "-Wno-format -Wno-format-security"
-    substituteInPlace tools/Makefile.linux \
+      substituteInPlace "tools/Makefile.linux" \
         --replace-warn "-lglut" "-lglut -lGL -lGLU"
+    ''
+    + lib.optionalString stdenv.hostPlatform.isDarwin ''
+      substituteInPlace "lib/Makefile.macosx" \
+                        "tools/Makefile.macosx" \
+                        "tools/jpeg/makefile.macosx" \
+                        "tools/zlib/Makefile.macosx" \
+        --replace-warn "gcc" "${stdenv.cc.targetPrefix}cc"
+      substituteInPlace "lib/Makefile.macosx" "tools/Makefile.macosx" "tools/tinyxml/Makefile.macosx" \
+        --replace-warn "g++" "${stdenv.cc.targetPrefix}c++"
     '';
 
   makeFlags = [