python/hooks/setuptools-build-hook.sh: use `--parallel` flag only for fresh setuptools

Without the change attempt to enable parallelist for `python2` packages
fails with unsupported `--parallel` flag for `setuptools`-based
packages:

$ nix build --no-link -f. --arg config '{enableParallelBuildingByDefault = true;}' xdg-utils
error: builder for '/nix/store/...-python2.7-setuptools-44.0.0.drv' failed with exit code 1;
last 10 log lines:
> no configure script, doing nothing
> Running phase: buildPhase
> Executing setuptoolsBuildPhase
> usage: nix_run_setup [global_opts] cmd1 [cmd1_opts] [cmd2 [cmd2_opts] ...]
> or: nix_run_setup --help [cmd1 cmd2 ...]
> or: nix_run_setup --help-commands
> or: nix_run_setup cmd --help
>
> error: option --parallel not recognized

pkgs/development/interpreters/python/hooks/default.nix

···
       propagatedBuildInputs = [ setuptools wheel ];
       substitutions = {
         inherit pythonInterpreter setuppy;
+        # python2.pkgs.setuptools does not support parallelism
+        setuptools_has_parallel = setuptools != null && lib.versionAtLeast setuptools.version "69";
       };
     } ./setuptools-build-hook.sh) {};
 

pkgs/development/interpreters/python/hooks/setuptools-build-hook.sh

···
 
 setuptoolsBuildPhase() {
     echo "Executing setuptoolsBuildPhase"
-    local args
+    local args setuptools_has_parallel=@setuptools_has_parallel@
     runHook preBuild
 
     cp -f @setuppy@ nix_run_setup
···
         args+="$setupPyGlobalFlags"
     fi
     if [ -n "$enableParallelBuilding" ]; then
-        setupPyBuildFlags+=" --parallel $NIX_BUILD_CORES"
+        if [ -n "$setuptools_has_parallel" ]; then
+            setupPyBuildFlags+=" --parallel $NIX_BUILD_CORES"
+        fi
     fi
     if [ -n "$setupPyBuildFlags" ]; then
         args+=" build_ext $setupPyBuildFlags"