use target_has_atomic instead of build script

[tyllmoritz]

The build_script didn't work for me when using a custom target [0], so I tried compiling radium with target_has_atomic.

This is my first pull request with rust, so please test this change.

I didn't check, for example, whether the data from target_has_atomic matches the logic from the build script.

Thanks

[0] https://lupyuen.github.io/articles/rust#custom-rust-target-for-bl602

[tyllmoritz]

The cfg(target_has_atomic) compiler attribute is stable now. [0]

TODO: README.md, Version-bump and docs. Am I missing something?

[0] https://github.com/rust-lang/rust/blob/master/RELEASES.md#version-1600-2022-04-07

[myrrlyn]

The v1 series raises MSRV to Rust 1.60 and uses cfg(target_has_atomic). I am working on publishing a bitvec release that incorporates this. You should be able to force the issue by applying

[patch.crates-io]
radium = "1.0" # or `1.1`

in your Cargo manifest.

I appreciate your willingness to write this patch. I am sorry that I haven't been in a position to work on this for the past year and change, but I am hopeful that this time I'll be able to keep it up.