[CI/Build]: make it possible to build with a free-threaded interpreter (#29241)

Signed-off-by: Ralf Gommers <ralf.gommers@gmail.com>
Co-authored-by: Cyrus Leung <tlleungac@connect.ust.hk>

setup.py

@@ -10,6 +10,7 @@ import re
 import shutil
 import subprocess
 import sys
+import sysconfig
 from pathlib import Path
 from shutil import which
 
@@ -74,9 +75,13 @@ def is_ninja_available() -> bool:
     return which("ninja") is not None
 
 
+def is_freethreaded():
+    return bool(sysconfig.get_config_var("Py_GIL_DISABLED"))
+
+
 class CMakeExtension(Extension):
     def __init__(self, name: str, cmake_lists_dir: str = ".", **kwa) -> None:
-        super().__init__(name, sources=[], py_limited_api=True, **kwa)
+        super().__init__(name, sources=[], py_limited_api=not is_freethreaded(), **kwa)
         self.cmake_lists_dir = os.path.abspath(cmake_lists_dir)