Fix "std" support status of some tier 3 targets
https://github.com/rust-lang/rust/pull/127265 marked targets with empty "std" support status as no-std targets in target-spec metadata:
> * Where a targets 'std' or 'host tools' support is listed as '?' in the rust docs, these are left as 'None' with this PR. The corresponding changes in cargo will only reject an attempt to build std if the 'std' field is 'Some(false)'. In the case it is 'None', cargo will continue trying to build
However, this is not accurate because "std" support status has a marker indicating that it is a no-std target. (empty status is just invalid.)
https://doc.rust-lang.org/nightly/rustc/platform-support.html#tier-3
> The `std` column in the table below has the following meanings:
>
> * ✓ indicates the full standard library is available.
> * \* indicates the target only supports [`no_std`] development.
> * ? indicates the standard library support is unknown or a work-in-progress.
>
> [`no_std`]: https://rust-embedded.github.io/book/intro/no-std.html
This PR fixes the status of targets whose "std" support status is currently set to empty and update target-spec metadata.
The new status is set based on the following criteria:
- Set to ✓ for targets that I regularly check in [rust-cross-toolchain](https://github.com/taiki-e/rust-cross-toolchain) that the `cargo test` works. (riscv32-unknown-linux-gnu,{riscv64,s390x}-unknown-linux-musl)
- Targets where `cargo run` works but `cargo test` does not work tend to have incomplete std support (e.g., riscv32 musl f3068b66e0), so I included them in the group below that means “work in progress” rather than in this group.
- Set powerpc64le FreeBSD to ✓ on both std and host_tools, because the [Rust package](https://www.freshports.org/lang/rust/) is available.
- Set to ? (which means "unknown" or “work in progress”) for all other affected targets because these are Linux, Android, FreeBSD, or Fuchsia, all of which are operating systems that support std if properly supported.
r? Noratrieb
cc ``@harmou01``
5dd102e2f8