pthread usage in pkg

Hey,

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] pthread_mutex_lock(&iota_wallet_bundle_essence_mutex);

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.