Refactor the features module (rust-lang#2592)

* Refactor the `features` module

Co-authored-by: Tshepang Mbambo <tshepang@gmail.com>

Author: pvdrz

bindgen-cli/options.rs

@@ -12,9 +12,9 @@ use std::process::exit;
 
 fn rust_target_help() -> String {
     format!(
-        "Version of the Rust compiler to target. Valid options are: {:?}. Defaults to {:?}.",
+        "Version of the Rust compiler to target. Valid options are: {:?}. Defaults to {}.",
         RUST_TARGET_STRINGS,
-        String::from(RustTarget::default())
+        RustTarget::default()
     )
 }
 

bindgen/codegen/mod.rs

@@ -4348,7 +4348,7 @@ fn unsupported_abi_diagnostic(
         .add_annotation(
             format!(
                 "The configured Rust version is {}.",
-                String::from(ctx.options().rust_target)
+                ctx.options().rust_target
             ),
             Level::Note,
         );