bpo-36763: Add _PyInitError functions (GH-13395)

* Add _PyInitError functions:

  * _PyInitError_Ok()
  * _PyInitError_Error()
  * _PyInitError_NoMemory()
  * _PyInitError_Exit()
  * _PyInitError_IsError()
  * _PyInitError_IsExit()
  * _PyInitError_Failed()

* frozenmain.c and _testembed.c now use functions rather than macros.
* Move _Py_INIT_xxx() macros to the internal API.
* Move _PyWstrList_INIT macro to the internal API.
diff --git a/PC/getpathp.c b/PC/getpathp.c
index 76d3a08..64aa1e0 100644
--- a/PC/getpathp.c
+++ b/PC/getpathp.c
@@ -80,6 +80,7 @@
 
 
 #include "Python.h"
+#include "pycore_coreconfig.h"
 #include "pycore_pystate.h"
 #include "osdefs.h"
 #include <wchar.h>