Error: undefined reference to __cxa_guard_acquire and __cxa_guard_release

You need to add the following flag:

-fno-threadsafe-statics

Do not emit the extra code to use the routines specified in the C++ ABI for thread-safe initialization of local statics. You can use this option to reduce code size slightly in code that doesn’t need to be thread-safe.

If you use the Arduino IDE, you need to edit the platform.txt of the board you’re using:

  • The file is located at %LOCALAPPDATA%\Arduino15\papckages\<brand>\hardware\<board>\<version>\platform.txt
  • The line to change is compiler.cpp.flags

Compiler flags in platform.txt

Global warming stripes by Professor Ed Hawkins (University of Reading)