Add a "std" feature to be friendlier for cargo nono.

.github/workflows/main.yml

@@ -30,8 +30,9 @@ jobs:
         cargo check --features v5_4
         cargo check --features v5_11
         cargo check --features "v3_2 netlink"
-        cargo check --no-default-features --features "v5_11 netlink"
-        cargo check --features no_std
+        cargo check --no-default-features --features "std v5_11 netlink"
+        cargo check --no-default-features --features "no_std v5_4 netlink"
+        cargo check --no-default-features --features "no_std general errno"
 
   gen:
     name: Update generated files

Cargo.toml

@@ -31,5 +31,6 @@ v4_4 = []
 v4_20 = []
 v5_4 = []
 v5_11 = []
-default = ["general", "errno"]
+default = ["std", "general", "errno"]
+std = []
 no_std = ['cty']

gen/src/main.rs

@@ -239,7 +239,8 @@ fn main() {
         }
     }
 
-    writeln!(cargo_toml, "default = [{}]", DEFAULT_FEATURES).unwrap();
+    writeln!(cargo_toml, "default = [\"std\", {}]", DEFAULT_FEATURES).unwrap();
+    writeln!(cargo_toml, "std = []").unwrap();
     writeln!(cargo_toml, "no_std = ['cty']").unwrap();
 
     // Reset the `linux` directory back to the original branch.

src/lib.rs

@@ -1,9 +1,7 @@
 #![allow(non_camel_case_types, non_upper_case_globals, non_snake_case)]
-#![no_std]
+#![cfg_attr(not(feature = "std"), no_std)]
 
-#[cfg(not(feature = "no_std"))]
-extern crate std;
-#[cfg(not(feature = "no_std"))]
+#[cfg(feature = "std")]
 use std::os::raw as ctypes;
 
 #[cfg(feature = "no_std")]