Update the help message for --rust-target

bindgen/features.rs

@@ -120,10 +120,6 @@ macro_rules! define_rust_targets {
             }
         }
 
-        #[cfg(feature = "__cli")]
-        /// Strings of allowed `RustTarget` values
-        pub(crate) const RUST_TARGET_STRINGS: &[&str] = &[$(concat!("1.", stringify!($minor)),)*];
-
         #[derive(Debug, Copy, Clone, Eq, PartialEq, Hash)]
         pub(crate) struct RustFeatures {
             $($(pub(crate) $feature: bool,)*)*

bindgen/options/cli.rs

@@ -3,7 +3,7 @@ use crate::{
     callbacks::{
         AttributeInfo, DeriveInfo, ItemInfo, ParseCallbacks, TypeKind,
     },
-    features::RUST_TARGET_STRINGS,
+    features::EARLIEST_STABLE_RUST,
     regex_set::RegexSet,
     Abi, AliasVariation, Builder, CodegenConfig, EnumVariation,
     FieldVisibilityKind, Formatter, MacroTypeVariation, NonCopyUnionStyle,
@@ -21,8 +21,7 @@ use std::{fs::File, process::exit};
 
 fn rust_target_help() -> String {
     format!(
-        "Version of the Rust compiler to target. Valid options are: {:?}. Defaults to {}.",
-        RUST_TARGET_STRINGS,
+        "Version of the Rust compiler to target. Any Rust version after {EARLIEST_STABLE_RUST} is supported. Defaults to {}.",
         RustTarget::default()
     )
 }