fix fallback checks for kernels without private futex support

for unknown syscall commands, the kernel produces ENOSYS, not EINVAL.

src/internal/pthread_impl.h

@@ -112,7 +112,7 @@ static inline void __wake(volatile void *addr, int cnt, int priv)
 {
 	if (priv) priv = 128;
 	if (cnt<0) cnt = INT_MAX;
-	__syscall(SYS_futex, addr, FUTEX_WAKE|priv, cnt) != -EINVAL ||
+	__syscall(SYS_futex, addr, FUTEX_WAKE|priv, cnt) != -ENOSYS ||
 	__syscall(SYS_futex, addr, FUTEX_WAKE, cnt);
 }