[esp_system]: added __cxx_eh_arena_size_get again
[esp_system]: added __cxx_eh_arena_size_get again

* This function has been accidentally removed.
  It is necessary to provide the emergency
  exception memory pool size for C++ code.
  Since our libstdc++ always has exceptions
  enabled, this function must exist here even if
  -fno-exception is set for user code.

espressif/esp-idf,espressif/esp-idf,espressif/esp-idf,espressif/esp-idf