cryptsetup-generator: add postFixup

This makes cryptsetup-generator link correctly
to the shared systemd library.

pkgs/os-specific/linux/systemd/cryptsetup-generator.nix

@@ -13,6 +13,17 @@ stdenv.lib.overrideDerivation systemd (p: {
     ninja systemd-cryptsetup systemd-cryptsetup-generator
   '';
 
+  # As ninja install is not used here, the rpath needs to be manually fixed.
+  # Otherwise the resulting binary doesn't properly link against systemd-shared.so
+  postFixup = ''
+    sharedLib=libsystemd-shared-${p.version}.so
+    for prog in `find $out -type f -executable`; do
+      (patchelf --print-needed $prog | grep $sharedLib > /dev/null) && (
+        patchelf --set-rpath `patchelf --print-rpath $prog`:"$out/lib/systemd" $prog
+      ) || true
+    done
+  '';
+
   installPhase = ''
     mkdir -p $out/lib/systemd/
     cp systemd-cryptsetup $out/lib/systemd/systemd-cryptsetup