Upgrade c++ standard

[balazsracz]

We'd like to move up in the c++ standard used. This issue thread is to record information about the different build environments and their compliance to various standard levels.

[balazsracz]

esp32 Arduino 3.3.0 uses ESP-IDF 5.5, and the flag it sets is a bit confusing:
-std=gnu++2b -fexceptions -fno-rtti -fuse-cxa-atexit -std=gnu++2a
This is from file packages/esp32/tools/esp32-arduino-libs/idf-release_v5.5-b66b5448-v1/esp32/flags/cpp_flags

[balazsracz]

Esp32 Arduino 3.2.0 does the same:
-std=gnu++2b -fexceptions -fno-rtti -fuse-cxa-atexit -std=gnu++2a

[balazsracz]

ESP-IDF 5.4 uses -std=gnu++2b

[balazsracz]

Arduino Adafruit SAMD core uses -std=gnu++11 which is not great.

[balazsracz]

Arduino stm32 2.11.0 uses -std=gnu++17

[balazsracz]

Arduino Uno R4 minima uses -std=gnu++17

[atanisoft]

The usage of gnu++2b in ESP-IDF is short for the GNU variant of C++23 as implemented by GCC 14.2.0. Likely compiler version should also be checked as there will likely be variation of support for the standards between versions.