rust: added extern crate self as kernel

This allows proc macros to refer to `::kernel`. This syntax is needed in
order to ensure that we refer to the true kernel crate instead of a
local module.

Signed-off-by: Benno Lossin <[email protected]>

Author: BennoLossin

rust/kernel/lib.rs

@@ -31,6 +31,9 @@
 #[cfg(not(CONFIG_RUST))]
 compile_error!("Missing kernel configuration for conditional compilation");
 
+// allow proc-macros to refer to `::kernel`.
+extern crate self as kernel;
+
 #[cfg(not(test))]
 #[cfg(not(testlib))]
 mod allocator;