gh-116749: Disable GIL by default in free-threaded build

Switch GIL to disabled by default in free-threaded build so that the
free-threaded CIs catch thread-safety issues.

Author: colesbury

Lib/test/test_cmd_line.py

@@ -884,7 +884,7 @@ def test_pythondevmode_env(self):
     def test_python_gil(self):
         cases = [
             # (env, opt, expected, msg)
-            (None, None, 'None', "no options set"),
+            (None, None, '0', "no options set"),
             ('0', None, '0', "PYTHON_GIL=0"),
             ('1', None, '1', "PYTHON_GIL=1"),
             ('1', '0', '0', "-X gil=0 overrides PYTHON_GIL=1"),

Lib/test/test_embed.py

@@ -534,7 +534,7 @@ class InitConfigTests(EmbeddingTestsMixin, unittest.TestCase):
     if support.Py_DEBUG:
         CONFIG_COMPAT['run_presite'] = None
     if support.Py_GIL_DISABLED:
-        CONFIG_COMPAT['enable_gil'] = -1
+        CONFIG_COMPAT['enable_gil'] = 0
     if MS_WINDOWS:
         CONFIG_COMPAT.update({
             'legacy_windows_stdio': 0,

Python/initconfig.c

@@ -847,7 +847,7 @@ _PyConfig_InitCompatConfig(PyConfig *config)
     config->code_debug_ranges = 1;
     config->cpu_count = -1;
 #ifdef Py_GIL_DISABLED
-    config->enable_gil = _PyConfig_GIL_DEFAULT;
+    config->enable_gil = _PyConfig_GIL_DISABLE;
 #endif
 }