feature: Add new API `Client::{try_acquire, support_try_acquire}` for non-blocking operation

[NobodyXu]

On unix, when the named fifo is used and on Windows, it is possible to acquire without blocking.

For named fifo on unix, we can simply set pipe to be non-blocking before reading.

https://github.com/rust-lang/cc-rs/blob/2f587f5561fb9c3c02e5c9e186b2bea98691608a/src/parallel/job_token/unix.rs#L113

On windows, we can use WaitForSingleObject(self.sem, 0):

https://github.com/rust-lang/cc-rs/blob/2f587f5561fb9c3c02e5c9e186b2bea98691608a/src/parallel/job_token/windows.rs#L44

On Linux, we can also applies an optimization, to turn an annoymous pipe into a named fifo:

https://github.com/rust-lang/cc-rs/blob/2f587f5561fb9c3c02e5c9e186b2bea98691608a/src/parallel/job_token/unix.rs#L77

Though that optimization is verified to be incorrect on macOS, opening /dev/fd/$fd seems to return the same file description.

[NobodyXu]

My proposal is add two new APIs to Client:

impl Client {
    fn try_acquire(&self) -> io::Result<Option<Acquired>>;

    fn supports_try_acquire(&self) -> bool;
}