Fix BSD and macOS builds w.r.t. pthread_setname_np (bug#38632)
pthread_setname_np takes only a single argument on BSD and macOS, and affects the current thread only. * configure.ac: Add check for single-argument pthread_setname_np * src/systhread.c (sys_thread_set_name): New (w32 and pthread versions). (sys_thread_create): Remove name argument and name-setting. (w32_beginthread_wrapper): Remove name-setting. * src/systhread.h (sys_thread_create, sys_thread_set_name): Update prototypes. * src/thread.c (run_thread): Call sys_thread_set_name. (Fmake_thread): Adapt call to sys_thread_create. * src/thread.h (struct thread_state): Adjust comment.