pthread_win32_process_attach_np was available in mingw32-pthreads but is no longer available after the upgrade to mingw32-winpthreads
Hmm, it is related to alertable asynchrone thread-cancelation. Hmm, I think this routine is simply not necessary in winpthread.
Could you try for your test to add
BOOL pthread_win32_process_attach_np (void)
I'm only compile-testing this. Adding what you suggested works, though pthread_win32_process_detach_np is only missing (forgot to mention in the initial report :-/ )