The compiler is now able to warn if an invalid attribute (e.g like a
feature) is not available.
See https://blog.rust-lang.org/2024/05/06/check-cfg.html for more
details.
Add build.rs files in the crates that use #cfg(fuzzing) to add fuzzing
to the list of valid cfg attributes.
Signed-off-by: Rob Bradford <rbradford@rivosinc.com>
