bpo-36763: Add _PyCoreConfig._config_version (GH-13065)

Add private _config_version field to _PyPreConfig and _PyCoreConfig to prepare future ABI compatibility.

Author: vstinner

Include/cpython/coreconfig.h

@@ -65,7 +65,12 @@ typedef struct {
 
 /* --- _PyPreConfig ----------------------------------------------- */
 
+#define _Py_CONFIG_VERSION 1
+
 typedef struct {
+ int _config_version; /* Internal configuration version,
+ used for ABI compatibility */
+
  /* If greater than 0, enable isolated mode: sys.path contains
  neither the script's directory nor the user's site-packages directory.
 
@@ -132,6 +137,7 @@ typedef struct {
 #define _PyPreConfig_INIT \
  (_PyPreConfig){ \
  _PyPreConfig_WINDOWS_INIT \
+ ._config_version = _Py_CONFIG_VERSION, \
  .isolated = -1, \
  .use_environment = -1, \
  .dev_mode = -1, \
@@ -141,9 +147,12 @@ typedef struct {
 /* --- _PyCoreConfig ---------------------------------------------- */
 
 typedef struct {
- int isolated;
- int use_environment;
- int dev_mode;
+ int _config_version; /* Internal configuration version,
+ used for ABI compatibility */
+
+ int isolated; /* Isolated mode? see _PyPreConfig.isolated */
+ int use_environment; /* Use environment variables? see _PyPreConfig.use_environment */
+ int dev_mode; /* Development mode? See _PyPreConfig.dev_mode */
 
  /* Install signal handlers? Yes by default. */
  int install_signal_handlers;
@@ -397,6 +406,7 @@ typedef struct {
 #define _PyCoreConfig_INIT \
  (_PyCoreConfig){ \
  _PyCoreConfig_WINDOWS_INIT \
+ ._config_version = _Py_CONFIG_VERSION, \
  .isolated = -1, \
  .use_environment = -1, \
  .dev_mode = -1, \