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

[musl] / src / thread / pthread_sigmask.c

#include <signal.h>
#include <errno.h>
#include <pthread.h>

int pthread_sigmask(int how, const sigset_t *set, sigset_t *old)
{
        int ret = sigprocmask(how, set, old);
        if (ret) return errno;
        return 0;
}