clingo-bootstrap: force setuptools through variant (#40866)

lib/spack/spack/bootstrap/core.py

@@ -291,6 +291,10 @@ def try_import(self, module: str, abstract_spec_str: str) -> bool:
         with spack_python_interpreter():
             # Add hint to use frontend operating system on Cray
             concrete_spec = spack.spec.Spec(abstract_spec_str + " ^" + spec_for_current_python())
+            # This is needed to help the old concretizer taking the `setuptools` dependency
+            # only when bootstrapping from sources on Python 3.12
+            if spec_for_current_python() == "python@3.12":
+                concrete_spec.constrain("+force_setuptools")
 
             if module == "clingo":
                 # TODO: remove when the old concretizer is deprecated  # pylint: disable=fixme