[libstdc++] Update avr libstdc++ submodule to C++20 version

[chris-durand]

Fix submodule commit

[chris-durand]

modm/src/modm/platform/i2c/i2c_master.hpp:81:34: error: 'floorf' is not a member of 'std'; did you mean 'floor'?
   81 |   constexpr float pre_raw = std::floorf(pre_part_raw) < 8 ? 0 : (pre_part_raw - 8) / pre;

It's correct that it doesn't work. libstdc++ does not provide std::*f C99 math functions in the std namespace, this is a gcc bug. Nasty macros in the AVR math.h C header like #define floorf floor made std::floorf accidentally compile. To fix a math function issue I undefined the macros in avr-libstdc++ <cmath> and replaced them with proper functions. Now the code above does not compile anymore.

To keep consistency between platforms I will not add the float variants but fix the modm AVR code to use the proper C++ native overloads.

[chris-durand]

The CI passes now, but there is still an issue to be fixed. Some math functions are still missing in namespace std but they are not used within the modm codebase. I'll add a test to trigger the problem.