cmocka uses non-standard function strdup
cmocka.c uses function strdup:
2545 msg = strdup(error_message);
However, strdup is not a standard C function and is generally not implemented by compilers that follow C99, C11 or C18. (The proprietary C99 compiler that my organization uses is one example :)
Replace the usage of strdup, or add a feature test macro to make it configurable.