`std=gnu++20` is shown as `201709`? @ NodeMCU:ESP8266:Arduino

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When I do

C:\Users\Max\.platformio\packages\toolchain-xtensa\bin\xtensa-lx106-elf-g++.exe  -v --help

I get

  -std=gnu++17                Conform to the ISO 2017 C++ standard with GNU
                              extensions.
  -std=gnu++1y                Deprecated in favor of -std=gnu++14.  Same as
                              -std=gnu++14.
  -std=gnu++1z                Deprecated in favor of -std=gnu++17.  Same as
                              -std=gnu++17.
  -std=gnu++20                Conform to the ISO 2020 C++ draft standard with
                              GNU extensions (experimental and incomplete
                              support).  Same as -std=gnu++2a.
  -std=gnu++2a                Conform to the ISO 2020 C++ draft standard with
                              GNU extensions (experimental and incomplete
                              support).

And further

C:\Users\Max\.platformio\packages\toolchain-xtensa\bin\xtensa-lx106-elf-g++.exe -std=gnu++20 -dM -E -x c++  - < NUL

gives

#define __cplusplus 201709L

So that version of the compiler definitely set the the __cplusplus macro to the the C++ 17 standard one. Likely because of the above warning that support is incomplete and experimental.

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