gradle: Fix gradle-2.12 on Linux to find libstdc++.so reference in native library.

pkgs/development/tools/build-managers/gradle/default.nix

@@ -4,6 +4,8 @@ rec {
   gradleGen = {name, src} : stdenv.mkDerivation rec {
     inherit name src;
 
+    buildPhase = ":";
+
     installPhase = ''
       mkdir -pv $out/lib/gradle/
       cp -rv lib/ $out/lib/gradle/
@@ -15,7 +17,21 @@ rec {
         --add-flags "-classpath $gradle_launcher_jar org.gradle.launcher.GradleMain"
     '';
 
-    phases = "unpackPhase installPhase";
+    fixupPhase = if (!stdenv.isLinux) then ":" else
+      let arch = if stdenv.is64bit then "amd64" else "i386"; in ''
+        mkdir patching
+        pushd patching
+        jar xf $out/lib/gradle/lib/native-platform-linux-${arch}-0.10.jar
+        patchelf --set-rpath "${stdenv.cc.cc}/lib:${stdenv.cc.cc}/lib64" net/rubygrapefruit/platform/linux-${arch}/libnative-platform.so
+        jar cf native-platform-linux-${arch}-0.10.jar .
+        mv native-platform-linux-${arch}-0.10.jar $out/lib/gradle/lib/
+        popd
+
+        # The scanner doesn't pick up the runtime dependency in the jar.
+        # Manually add a reference where it will be found.
+        mkdir $out/nix-support
+        echo ${stdenv.cc.cc} > $out/nix-support/manual-runtime-dependencies
+      '';
 
     buildInputs = [ unzip jdk makeWrapper ];