Needed to work with mio v0.6.22

1952: Update CI name; replace with GitHub Actions

`@lzutao` fixes #1952 , please test

Implement accept4 on Android as raw syscall.

This PR implements `accept4()` on Android using `syscall()` instead of the `accept4()` wrapper.

This is done because the `accept4()` wrapper wasn't added to Androids `libc` until version 5.0 (API level 21). By using `syscall` directly, `accept4` will also work on older  Android versions.

The kernel itself has supported it since Linux 2.6.28, which was shipped with stock Android since version 1.6 already: https://en.wikipedia.org/wiki/Android_version_history#Android_1.6_Donut_(API_4)

At the moment, the CI for the rust repo still uses API level 14. Although I also opened a PR to bump that too: https://github.com/rust-lang/rust/pull/78601. However, it might make sense to keep the old API level in CI if this is merged.

This avoids relying on Android 5.0 / API level 21. The Linux kernel used
by Android supports the syscall (except in truly ancient Android
versions), but the Android libc did not expose a wrapper.

Adding dl_iterate_phdr function to uclibc

Adding dl_iterate_phdr function and related structs and types to the
uclibc module as per the file include/link.h found in the uClibc-ng
repository as of version 1.0.36. This is necessary in order for rust to
work with a new target armv7-unknown-linux-uclibceabihf.

Adding dl_iterate_phdr function and related structs and types to the
uclibc module as per the file include/link.h found in the uClibc-ng
repository as of version 1.0.36. This is necessary in order for rust to
work with a new target armv7-unknown-linux-uclibceabihf.

Update to FreeBSD 12.2

https://www.freebsd.org/releases/12.2R/announce.html