It may be unclear for readers which upstream Rust version these files
are based on. They may be unaware that they are intended to match the
minimum (and only, so far) supported version of Rust in the kernel.

Thus clarify it.

Reviewed-by: Benno Lossin <benno.lossin@proton.me>
Reviewed-by: Björn Roy Baron <bjorn3_gh@protonmail.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
Tested-by: Ariel Miculas <amiculas@cisco.com>
Tested-by: David Gow <davidgow@google.com>
Tested-by: Boqun Feng <boqun.feng@gmail.com>
Link: https://lore.kernel.org/r/20230418214347.324156-2-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

This customizes the subset of the Rust standard library `alloc` that
was just imported as-is, mainly by:

  - Adding SPDX license identifiers.

  - Skipping modules (e.g. `rc` and `sync`) via new `cfg`s.

  - Adding fallible (`try_*`) versions of existing infallible methods
    (i.e. returning a `Result` instead of panicking).

    Since the standard library requires stable/unstable attributes,
    these additions are annotated with:

        #[stable(feature = "kernel", since = "1.0.0")]

    Using "kernel" as the feature allows to have the additions
    clearly marked. The "1.0.0" version is just a placeholder.

    (At the moment, only one is needed, but in the future more
    fallible methods will be added).

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Co-developed-by: Alex Gaynor <alex.gaynor@gmail.com>
Signed-off-by: Alex Gaynor <alex.gaynor@gmail.com>
Co-developed-by: Wedson Almeida Filho <wedsonaf@google.com>
Signed-off-by: Wedson Almeida Filho <wedsonaf@google.com>
Co-developed-by: Gary Guo <gary@garyguo.net>
Signed-off-by: Gary Guo <gary@garyguo.net>
Co-developed-by: Matthew Bakhtiari <dev@mtbk.me>
Signed-off-by: Matthew Bakhtiari <dev@mtbk.me>
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>