Std read-write lock support and adaptation std fs

[weiwenhao]

fn main() {
    var f = fs.open('./test.txt', syscall.O_RDONLY, 0)

    for int i = 0; i < 10; i += 1 {
        go fn():void! {
            var c = client.multipart_t_new()
            var parts = c.text('username', 'nature user')
                 .text('message', 'hello from nature!')
                 .file('testfile', 'test.txt', f.content())
        }()
    }

    co.sleep(1000)
}

Operations like this can cause unpredictable crashes because only one coroutine can exist in fd at a time, and using fd concurrently can lead to abnormal crashes.