SOLVED... thanks to https://github.com/arduino/arduino-cli/issues/1002

It was just a "Win10 too long path" issue

hi there
I'm facing a similar problem of:

Re: Error compiling for board M5Stack-Paper.

I'm on Arduino 1.8.13, on a Win10 machine. I followed the procedure described in https://docs.m5stack.com/en/arduino/arduino_core2_development so using board definition at https://m5stack.oss-cn-shenzhen.aliyuncs.com/resource/arduino/package_m5stack_index.json

I'm on board version 1.0.7 bundled with xtensa
"version": "1.22.0-80-g6c4433a-5.2.0",
"name": "xtensa-esp32-elf-gcc"

I'm trying to compile rtc_wakeup example and get exactly same error reported in the linked topic.

"C:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\tools\xtensa-esp32-elf-gcc\1.22.0-80-g6c4433a-5.2.0/bin/xtensa-esp32-elf-g++" -DESP_PLATFORM "-DMBEDTLS_CONFIG_FILE="mbedtls/esp_config.h"" -DHAVE_CONFIG_H -DGCC_NOT_5_2_0=0 -DWITH_POSIX "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/config" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/app_trace" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/app_update" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/asio" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/bootloader_support" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/bt" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/coap" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/console" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/driver" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/esp-tls" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/esp32" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/esp_adc_cal" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/esp_event" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/esp_http_client" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/esp_http_server" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/esp_https_ota" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/esp_ringbuf" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/ethernet" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/expat" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/fatfs" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/freemodbus" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/freertos" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/heap" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/idf_test" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/jsmn" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/json" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/libsodium" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/log" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/lwip" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/mbedtls" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/mdns" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/micro-ecc" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/mqtt" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/newlib" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/nghttp" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/nvs_flash" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/openssl" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/protobuf-c" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/protocomm" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/pthread" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/sdmmc" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/smartconfig_ack" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/soc" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/spi_flash" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/spiffs" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/tcp_transport" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/tcpip_adapter" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/ulp" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/vfs" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/wear_levelling" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/wifi_provisioning" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/wpa_supplicant" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/xtensa-debug-module" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/esp-face" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/esp32-camera" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/esp-face" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4/tools/sdk/include/fb_gfx" -std=gnu++11 -Os -g3 -Wpointer-arith -fexceptions -fstack-protector -ffunction-sections -fdata-sections -fstrict-volatile-bitfields -mlongcalls -nostdlib -w -Wno-error=maybe-uninitialized -Wno-error=unused-function -Wno-error=unused-but-set-variable -Wno-error=unused-variable -Wno-error=deprecated-declarations -Wno-unused-parameter -Wno-unused-but-set-parameter -Wno-missing-field-initializers -Wno-sign-compare -fno-rtti -c -w -x c++ -E -CC -DF_CPU=240000000L -DARDUINO=10813 -DARDUINO_M5STACK_Core2 -DARDUINO_ARCH_ESP32 "-DARDUINO_BOARD="M5STACK_Core2"" "-DARDUINO_VARIANT="m5stack_core2"" -DESP32 -DCORE_DEBUG_LEVEL=0 -DBOARD_HAS_PSRAM -mfix-esp32-psram-cache-issue "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4\cores\esp32" "-IC:\userdata\Program Files\arduino-windows\portable\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4\variants\m5stack_core2" "C:\Users\michelepa\AppData\Local\Temp\arduino_build_353905\sketch\rtc_wakeup.ino.cpp" -o nul -DARDUINO_LIB_DISCOVERY_PHASE
Alternatives for bits/c++config.h: []
ResolveLibrary(bits/c++config.h)
-> candidates: []
In file included from c:\userdata\program files\arduino-windows_portable_\arduino-1.8.13\portable\packages\m5stack\tools\xtensa-esp32-elf-gcc\1.22.0-80-g6c4433a-5.2.0\xtensa-esp32-elf\include\c++\5.2.0\algorithm:60:0,
from C:\userdata\Program Files\arduino-windows_portable_\arduino-1.8.13\portable\packages\m5stack\hardware\esp32\1.0.4\cores\esp32/Arduino.h:142,
from C:\Users\michelepa\AppData\Local\Temp\arduino_build_353905\sketch\rtc_wakeup.ino.cpp:1:
c:\userdata\program files\arduino-windows_portable_\arduino-1.8.13\portable\packages\m5stack\tools\xtensa-esp32-elf-gcc\1.22.0-80-g6c4433a-5.2.0\xtensa-esp32-elf\include\c++\5.2.0\utility:68:28: fatal error: bits/c++config.h: No such file or directory
compilation terminated.
exit status 1

I have both a M5Stack Core2 and Lora868 moduel infront of me right now.
The core module has been disassembled in 2 parts (3 considering the sensor module by removing the 4 screws. To do so I also disconnected the 2 whire battery connection between the battery, sticked to the grey backplane module and the main board. Now the Lora blue module can be connected to the main core board (the white one). It fit perfectly. Now it is the turn of the back plain but I can see at least two problems here:

1. there's no way to connect the battery back to the mainboard now that the lora module is in between. Maybe I can drill the lora board PCD and sacrifice a couple of empty pcb vias there or add an additional couple of wire segments to go through them.
2. the battery or the grey plastic frame on the back plain mechanically hit the Lora module metal shield. This second one seems more difficult to fix.

The result is that the backplane cannot be reconnected to the sandwich if the Lora module is in between.

Any idea? Are a couple of photos useful here?