Revert "PyAPI: point sys.executable to the Python binary"

This reverts commit 04c5471cee.

This causes Blender not to start on some systems.

source/blender/python/intern/bpy_app.c

@@ -292,13 +292,36 @@ static int bpy_app_global_flag_set__only_disable(PyObject *UNUSED(self),
   return bpy_app_global_flag_set(NULL, value, closure);
 }
 
+#define BROKEN_BINARY_PATH_PYTHON_HACK
+
 PyDoc_STRVAR(bpy_app_binary_path_python_doc,
-             "String, the path to the python executable (read-only). "
-             "Deprecated! Use ``sys.executable`` instead.");
-static PyObject *bpy_app_binary_path_python_get(PyObject *UNUSED(self), void *UNUSED(closure))
+             "String, the path to the python executable (read-only)");
+static PyObject *bpy_app_binary_path_python_get(PyObject *self, void *UNUSED(closure))
 {
-  PyErr_Warn(PyExc_RuntimeWarning, "Use 'sys.executable' instead of 'binary_path_python'!");
-  return Py_INCREF_RET(PySys_GetObject("executable"));
+  /* refcount is held in BlenderAppType.tp_dict */
+  static PyObject *ret = NULL;
+
+  if (ret == NULL) {
+    /* only run once */
+    char fullpath[1024];
+    BKE_appdir_program_python_search(
+        fullpath, sizeof(fullpath), PY_MAJOR_VERSION, PY_MINOR_VERSION);
+    ret = PyC_UnicodeFromByte(fullpath);
+#ifdef BROKEN_BINARY_PATH_PYTHON_HACK
+    Py_INCREF(ret);
+    UNUSED_VARS(self);
+#else
+    PyDict_SetItem(
+        BlenderAppType.tp_dict,
+        /* XXX BAAAADDDDDD! self is not a PyDescr at all! it's bpy.app!!! */ PyDescr_NAME(self),
+        ret);
+#endif
+  }
+  else {
+    Py_INCREF(ret);
+  }
+
+  return ret;
 }
 
 PyDoc_STRVAR(bpy_app_debug_value_doc,