[PATCH] kbuild: rust: add rustc-min-version support function

[Fiona Behrens]

Miguel Ojeda <ojeda at kernel.org> writes:

> Introduce `rustc-min-version` support function that mimics
> `{gcc,clang}-min-version` ones, following commit 88b61e3bff93
> ("Makefile.compiler: replace cc-ifversion with compiler-specific macros").
>
> In addition, use it in the first use case we have in the kernel (which
> was done independently to minimize the changes needed for the fix).
>
> Signed-off-by: Miguel Ojeda <ojeda at kernel.org>

Reviewed-by: Fiona Behrens <me at Kloenk.dev>