[RFC] rust target change to riscv64a23

[laokz]

Rust riscv64a23-unknown-linux-gnu and riscv64gc-unknown-linux-gnu are both tier2 targets except that rva23 target has no offical published host tools[1]. From rust team discussions[2], It is OK to promote rva23 target to the same position as rv64gc in theory, the only barrier is "no-hardware-available".

We are focused on RVA23 profile and there is already some real hadware. So I think it is nature to switch to rva23 target in our project.

I've tested the changes a little by using rva23 rust to build itself, rust app[3], running and check small example binaries. It worked as expected.

1. https://doc.rust-lang.org/rustc/platform-support/riscv64a23-unknown-linux-gnu.html#riscv64a23-unknown-linux-gnu
2. Promote riscv64a23-unknown-linux-gnu to Tier 2 with host tools rust-lang/compiler-team#910
3. https://build.openruyi.cn/package/show/home:laokz:branches:openruyi/Bear

[wzssyqa]

Yes. I agree that it's time for us to use riscv64a23-unknown-linux-gnu for rustc as default now.

[yyjeqhc]

I agree with this change.

Since the Rust target support is already available and we have real hardware for validation, this looks like a reasonable direction. The migration may still expose some compatibility issues in packages or build scripts, so we should be prepared for the follow-up fixes and rebuild tests.

[laokz]

OK. It seems no objections there. I'll commit the change later. Thanks all your comments.