Revive `i686-linux-android` CI

Fixes #1765

Fix aarch64-linux-android target CI

Add deprecation notice to `af_alg_iv::as_slice` and trait implementations that depend on it

These trait implementations exposed an unsound API (see https://github.com/rust-lang/libc/issues/1501).

process_vm_readv, process_vm_writev should be available on android

process_vm_readv and process_vm_writev generally return -EPERM(-1) when used in android, however the syscalls work fine when running under privileged shell.
The following was tested(with modified nix) on Android 9/10 running Linux Kernel 4.9 on a SDM 845 phone:

```
fn read_mem_real(pid: i32, addr: usize, vsize: usize) -> Result<Vec<u8>, String> {
    let mut res = vec![0; vsize];
    let riovec: [RemoteIoVec; 1] = [RemoteIoVec {base: addr, len: vsize}];

    match process_vm_readv(Pid::from_raw(pid), &[IoVec::from_mut_slice(&mut res)], &riovec) {
        Err(e) => {
            log::info!("ERR {}", e);
            return Err(e.to_string());
        },
        Ok(_) => {
            return Ok(res);
        }
    }
}
```

This will work fine when run under su shell.

Signed-off-by: rupansh-arch <rupanshsekar@hotmail.com>

These trait implementations exposed an unsound API (see
https://github.com/rust-lang/libc/issues/1501)

Allow contributors to label issues via rustbot

Now bors suggests contributors label PRs with the status labels, e.g.:

https://github.com/rust-lang/libc/pull/1902#issuecomment-702337160

This allows it, and for issues as well.

Add clock_nanosleep to freebsd and netbsd

fixes #1921

Tweak GHA config to reduce bors time

So, "bors time" with the current config is slow a bit (~ 1h30m). We could reduce this by separating style check and docs generation, tweaking `max-parallel`, let's try it out!

Upload documentation to gh-pages from GHA

I missed this on #1918 

Only style check on PRs to reduce CI time

I think generating docs on PR jobs is overkill, just style check is enough.

Serial Experiments GitHub Actions

Let's start the party to close #1582.