rust: add `build_error` crate

maillist inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I5J75G
CVE: NA

Reference: https://lore.kernel.org/rust-for-linux/CANiq72nDcJLSB3pLhkdqGdLitfmqqCUVVfkY5EjP9AcwVv9B4A@mail.gmail.com/T/#t

--------------------------------

The `build_error` crate provides the `build_error` function which
is then used to provide the `build_error!` and the `build_assert!`
macros.

`build_assert!` is intended to be used when `static_assert!` cannot
be used, e.g. when the condition refers to generic parameters or
parameters of an inline function.
Co-developed-by: NAlex Gaynor <alex.gaynor@gmail.com>
Signed-off-by: NAlex Gaynor <alex.gaynor@gmail.com>
Co-developed-by: NWedson Almeida Filho <wedsonaf@google.com>
Signed-off-by: NWedson Almeida Filho <wedsonaf@google.com>
Signed-off-by: NGary Guo <gary@garyguo.net>
Co-developed-by: NMiguel Ojeda <ojeda@kernel.org>
Signed-off-by: NMiguel Ojeda <ojeda@kernel.org>
Signed-off-by: NWeilong Chen <chenweilong@huawei.com>

rust/build_error.rs

+// SPDX-License-Identifier: GPL-2.0
+
+//! Build-time error.
+//!
+//! This crate provides a function `build_error`, which will panic in
+//! compile-time if executed in const context, and will cause a build error
+//! if not executed at compile time and the optimizer does not optimise away the
+//! call.
+//!
+//! It is used by `build_assert!` in the kernel crate, allowing checking of
+//! conditions that could be checked statically, but could not be enforced in
+//! Rust yet (e.g. perform some checks in const functions, but those
+//! functions could still be called in the runtime).
+
+#![no_std]
+
+/// Panics if executed in const context, or triggers a build error if not.
+#[inline(never)]
+#[cold]
+#[no_mangle]
+#[track_caller]
+pub const fn build_error(msg: &'static str) -> ! {
+    panic!("{}", msg);
+}
+
+#[cfg(CONFIG_RUST_BUILD_ASSERT_WARN)]
+#[link_section = ".gnu.warning.build_error"]
+#[used]
+static BUILD_ERROR_WARNING: [u8; 45] = *b"call to build_error present after compilation";