bpo-36301: Add _PyRuntime.pre_initialized (GH-12457)

* Add _PyRuntime.pre_initialized: set to 1 when Python
  is pre-initialized
* Add _Py_PreInitialize() and _Py_PreInitializeFromPreConfig().
* _PyCoreConfig_Read() now calls  _Py_PreInitialize().
* Move _PyPreConfig_GetGlobalConfig() and
  _PyCoreConfig_GetGlobalConfig() calls from main.c to preconfig.c
  and coreconfig.c.
diff --git a/Include/cpython/pylifecycle.h b/Include/cpython/pylifecycle.h
index 3bffc80..1caeb98 100644
--- a/Include/cpython/pylifecycle.h
+++ b/Include/cpython/pylifecycle.h
@@ -14,6 +14,10 @@
 
 /* PEP 432 Multi-phase initialization API (Private while provisional!) */
 
+PyAPI_FUNC(_PyInitError) _Py_PreInitialize(void);
+PyAPI_FUNC(_PyInitError) _Py_PreInitializeFromPreConfig(
+    _PyPreConfig *preconfig);
+
 PyAPI_FUNC(_PyInitError) _Py_InitializeCore(
     PyInterpreterState **interp,
     const _PyCoreConfig *);