I still have the issue with posix threads in my package. The compiler is not able to find a reference for pthread_mutex_lock
error: implicit declaration of function 'pthread_mutex_lock'; did you mean 'pthread_atfork'? [-Werror=implicit-function-declaration]
The example is available here: https://github.com/Citrullin/RIOT/blob/iota_new_implementation/examples/iota_transaction_node/main.c
The packages includes pthreads as module: https://github.com/Citrullin/RIOT/blob/iota_new_implementation/pkg/iota-wallet/Makefile.dep
I don’t have an idea how to solve that.