@mfalkvidd Thanks, that solution worked and sorry I should have found that posting myself of course.

FYI, for loading the ESP8266 Board definitions the usual URL https://arduino.esp8266.com/stable/package_esp8266com_index.json did not work for me anymore. Instead I had to use https://github.com/esp8266/Arduino/releases/download/2.4.2/package_esp8266com_index.json

Hi Roland, yes in the end I managed to finish compiling without error. I tried with a Windows-10 machine, a Linux Ubuntu laptop and a RaspberryPi-4 and various versions of Arduino IDE, MySensors and NodeManager. Unfortunately, thereafter I got problems running the sketch and because of too little understanding of the NodeManager programming gave up for the time being. I dismantled my setup and cannot remember which combination of soft/hardware gave me compiling success in the end. It now seems that at least part of my problems may be due to the fact that I did not yet have a NRF24L01 hooked up to the ESP8266 so I will give things another try in the future.

@mfalkvidd Thanks, that solution worked and sorry I should have found that posting myself of course.

FYI, for loading the ESP8266 Board definitions the usual URL https://arduino.esp8266.com/stable/package_esp8266com_index.json did not work for me anymore. Instead I had to use https://github.com/esp8266/Arduino/releases/download/2.4.2/package_esp8266com_index.json

Re: Building a WiFi Gateway using ESP8266

After failing to install the GatewayESP8266.ino on my Node MCU from Windows 10, I tried to install the sketch from Linux Ubuntu with MySensors library v.2.3.1 and ESP8266 Board definitions v.2.4.1 but again a compiling error shows up in Arduino IDE v.1.8.9:

Arduino: 1.8.9 (Linux), Board: "NodeMCU 1.0 (ESP-12E Module), 80 MHz, 4M (1M SPIFFS), v2 Lower Memory, Disabled, None, Only Sketch, 115200"

In file included from /home/Name/Arduino/libraries/MySensors/MySensors.h:441:0,
                 from /home/Name/Arduino/GatewayESP8266/GatewayESP8266.ino:119:
/home/Name/Arduino/libraries/MySensors/hal/architecture/ESP8266/MyMainESP8266.cpp:33:23: fatal error: gdb_hooks.h: No such file or directory
 #include "gdb_hooks.h"
                       ^
compilation terminated.
exit status 1
Error compiling for board NodeMCU 1.0 (ESP-12E Module).

Anybody with a suggestion how to solve this?

@mfalkvidd : Thanks for the quick reply. Unfortunately a restart of the Arduino IDE did not solve the problem.
I spotted a warning for Arduino IDE 1.8.10 (https://forum.mysensors.org/topic/10763/arduino-ide-1-8-10-warning) and tried 1.8.9 and 1.8.8 but again no luck with these.

Are my Tools settings correct?

The problem I am having with compiling the sketch GatewayESP8266 to a NodeMCU board is the same as mentioned by mcrahr in his original post:
exit status 1
Error compiling for board NodeMCU 1.0 (ESP-12E Module)
(and 64 pages of error messages)

In my case the environment is:
Arduino IDE 1.8.10 on Windows 10 PC
MySensors library 2.3.1
Board definitions ESP8266 2.6.0

As suggested I have downgraded the board definitions to version 2.4.1 but that did not help.
Also using the definition GenericESP8266 Module was not successful
The simple Blink sketch compiles and uploads without problem.

Suggestions for a solution are welcome.