cut out a syscall on thread creation in the case where guard size is 0

[musl] / src / thread / pthread_barrierattr_setpshared.c

#include "pthread_impl.h"

int pthread_barrierattr_setpshared(pthread_barrierattr_t *a, int pshared)
{
        *a = !!pshared;
        return 0;
}