bpo-36763: _PyInitError always use int for exitcode (GH-13360)

We cannot use "unsigned int" for exitcode on Windows, since
Py_Main() and _Py_RunMain() always return an "int".

Changes:

* _PyPathConfig_ComputeSysPath0() now returns -1 if an exception is
  raised.
* pymain_run_python() no longer uses _PyInitError but display the
  exception and set exitcode to 1 in case of error.
* Fix _Py_RunMain(): return an exitcode rather than calling
  exit() on pymain_run_python() failure.
* _Py_ExitInitError() no longer uses ExitProcess() on Windows, use
  exit() on all platforms.
* _Py_ExitInitError() now fails with a fatal error if 'err' is not an
  error not an exit.

Modules/main.c

@@ -130,7 +130,7 @@ pymain_sys_path_add_path0(PyInterpreterState *interp, PyObject *path0)
     if (sysdict != NULL) {
         sys_path = _PyDict_GetItemIdWithError(sysdict, &PyId_path);
         if (sys_path == NULL && PyErr_Occurred()) {
-            goto error;
+            return -1;
         }
     }
     else {
@@ -138,17 +138,13 @@ pymain_sys_path_add_path0(PyInterpreterState *interp, PyObject *path0)
     }
     if (sys_path == NULL) {
         PyErr_SetString(PyExc_RuntimeError, "unable to get sys.path");
-        goto error;
+        return -1;
     }
 
     if (PyList_Insert(sys_path, 0, path0)) {
-        goto error;
+        return -1;
     }
     return 0;
-
-error:
-    PyErr_Print();
-    return -1;
 }
 
 
@@ -443,11 +439,9 @@ pymain_repl(_PyCoreConfig *config, PyCompilerFlags *cf, int *exitcode)
 }
 
 
-static _PyInitError
+static void
 pymain_run_python(int *exitcode)
 {
-    _PyInitError err;
-
     PyInterpreterState *interp = _PyInterpreterState_GET_UNSAFE();
     /* pymain_run_stdin() modify the config */
     _PyCoreConfig *config = &interp->core_config;
@@ -464,22 +458,20 @@ pymain_run_python(int *exitcode)
 
     if (main_importer_path != NULL) {
         if (pymain_sys_path_add_path0(interp, main_importer_path) < 0) {
-            err = _Py_INIT_EXIT(1);
-            goto done;
+            goto error;
         }
     }
     else if (!config->isolated) {
         PyObject *path0 = NULL;
-        if (_PyPathConfig_ComputeSysPath0(&config->argv, &path0)) {
-            if (path0 == NULL) {
-                err = _Py_INIT_NO_MEMORY();
-                goto done;
-            }
+        int res = _PyPathConfig_ComputeSysPath0(&config->argv, &path0);
+        if (res < 0) {
+            goto error;
+        }
 
+        if (res > 0) {
             if (pymain_sys_path_add_path0(interp, path0) < 0) {
                 Py_DECREF(path0);
-                err = _Py_INIT_EXIT(1);
-                goto done;
+                goto error;
             }
             Py_DECREF(path0);
         }
@@ -508,11 +500,14 @@ pymain_run_python(int *exitcode)
     }
 
     pymain_repl(config, &cf, exitcode);
-    err = _Py_INIT_OK();
+    goto done;
+
+error:
+    PyErr_Print();
+    *exitcode = 1;
 
 done:
     Py_XDECREF(main_importer_path);
-    return err;
 }
 
 
@@ -578,17 +573,14 @@ _Py_RunMain(void)
 {
     int exitcode = 0;
 
-    _PyInitError err = pymain_run_python(&exitcode);
-    if (_Py_INIT_FAILED(err)) {
-        pymain_exit_error(err);
-    }
-
+    pymain_run_python(&exitcode);
     if (Py_FinalizeEx() < 0) {
         /* Value unlikely to be confused with a non-error exit status or
            other special meaning */
         exitcode = 120;
     }
 
+done:
     pymain_free();
 
     if (_Py_UnhandledKeyboardInterrupt) {
@@ -603,6 +595,10 @@ static int
 pymain_main(_PyArgv *args)
 {
     _PyInitError err = pymain_init(args);
+    if (_Py_INIT_IS_EXIT(err)) {
+        pymain_free();
+        return err.exitcode;
+    }
     if (_Py_INIT_FAILED(err)) {
         pymain_exit_error(err);
     }