x2goserver: fix build (#426799)

pkgs/by-name/x2/x2goserver/package.nix

@@ -117,6 +117,8 @@ stdenv.mkDerivation {
     do
       substituteInPlace $i --replace '/etc/x2go' '/var/lib/x2go/conf'
     done
+    substituteInPlace x2goserver/Makefile \
+      --replace-fail "\$(DESTDIR)/etc" "\$(DESTDIR)/\$(ETCDIR)"
     substituteInPlace x2goserver/sbin/x2gocleansessions \
       --replace '/var/run/x2goserver.pid' '/var/run/x2go/x2goserver.pid'
     substituteInPlace x2goserver/sbin/x2godbadmin --replace 'user="x2gouser"' 'user="x2go"'
@@ -126,16 +128,16 @@ stdenv.mkDerivation {
   '';
 
   makeFlags = [
-    "PREFIX=/"
-    "NXLIBDIR=${nx-libs}/lib/nx"
+    "PREFIX=${placeholder "out"}"
+    "ETCDIR=${placeholder "out"}/etc/x2go"
+    "NXLIBDIR=${placeholder "out"}"
   ];
 
-  installFlags = [ "DESTDIR=$(out)" ];
-
   postInstall = ''
     mv $out/etc/x2go/x2goserver.conf{,.example}
     mv $out/etc/x2go/x2goagent.options{,.example}
     ln -sf ${nx-libs}/bin/nxagent $out/bin/x2goagent
+    ln -sf ${nx-libs}/share/nx/VERSION.nxagent $out/share/x2go/versions/VERSION.x2goserver-x2goagent
     for i in $out/sbin/x2go* $(find $out/bin -type f) \
       $(ls $out/lib/x2go/x2go* | grep -v x2gocheckport)
     do