Fix test workload warnings for no_std.

Fix missing cargo-clippy feature warning.

Fix unused imports / functions warnings when testing no_std.

Fix unused mut warning in rbpf_plugin.rs.

Fix unused Error, Errorkind import warning.

Signed-off-by: SzymonKubica <szymo.kubica@gmail.com>

Cargo.toml

@@ -49,6 +49,7 @@ hex = "0.4.3"
 
 [features]
 default = ["std"]
+cargo-clippy = []
 std = ["dep:time", "dep:libc", "combine/std"]
 cranelift = [
     "dep:cranelift-codegen",

examples/rbpf_plugin.rs

@@ -15,6 +15,7 @@ fn _unwind(a: u64, _b: u64, _c: u64, _d: u64, _e: u64) -> u64
 // It reads the program from stdin.
 fn main() {
     let mut args: Vec<String> = std::env::args().collect();
+    #[allow(unused_mut)] // In no_std the jit variable isn't mutated.
     let mut jit : bool = false;
     let mut cranelift : bool = false;
     let mut program_text = String::new();

tests/misc.rs

@@ -19,9 +19,11 @@
 
 extern crate rbpf;
 
+#[cfg(feature = "std")]
 use rbpf::lib::{Error, ErrorKind};
 #[cfg(feature = "std")]
 use rbpf::assembler::assemble;
+#[cfg(feature = "std")]
 use rbpf::helpers;
 
 // The following two examples have been compiled from C with the following command:
@@ -573,10 +575,12 @@ fn test_vm_exec_no_program() {
     assert_eq!(vm.execute_program().unwrap(), 0xBEE);
 }
 
+#[cfg(feature = "std")]
 fn verifier_success(_prog: &[u8]) -> Result<(), Error> {
     Ok(())
 }
 
+#[cfg(feature = "std")]
 fn verifier_fail(_prog: &[u8]) -> Result<(), Error> {
     Err(Error::new(ErrorKind::Other,
                    "Gaggablaghblagh!"))