Emit expected cfg instructions in build.rs

It is no longer necessary to use the temporary workaround in Cargo.toml of
specifying the expected values in unexpected_cfgs table.

Remove the unexpected_cfgs deny from Cargo.toml entirely. unexpected_cfgs
is warn by default, and Cargo.toml already specifies that all warnings
should be denied.

Signed-off-by: the Mulhern <amulhern@amulhern.bos.csb>

Author: the Mulhern

Cargo.toml

@@ -51,9 +51,6 @@ future_incompatible = { level = "deny", priority = 1 }
 unused = { level = "deny", priority = 2}
 rust_2018_idioms = { level = "deny", priority = 3 }
 nonstandard_style = { level = "deny", priority = 4 }
-unexpected_cfgs = { level = "deny", check-cfg = [
-  'cfg(cryptsetup23supported)', 'cfg(cryptsetup24supported)', 'cfg(cryptsetup27supported)'
-] }
 
 [lints.clippy]
 all = { level = "deny" }

build.rs

@@ -18,13 +18,16 @@ fn main() {
         Ok(l) => Version::parse(&l.version).unwrap(),
         Err(e) => panic!("Bindings require at least cryptsetup-2.2.0: {e}"),
     };
-    for ver in SUPPORTED_VERSIONS.iter().take_while(|ver_string| {
-        let iter_version = Version::parse(ver_string).expect("Could not parse version");
-        version >= iter_version
-    }) {
-        println!(
-            "cargo:rustc-cfg=cryptsetup{}supported",
-            ver.split('.').take(2).collect::<Vec<_>>().join("")
+    for ver_string in SUPPORTED_VERSIONS.iter() {
+        let version_cfg = format!(
+            "cryptsetup{}supported",
+            ver_string.split('.').take(2).collect::<Vec<_>>().join("")
         );
+        println!("cargo::rustc-check-cfg=cfg({version_cfg},)");
+
+        let iter_version = Version::parse(ver_string).expect("Could not parse version");
+        if version >= iter_version {
+            println!("cargo:rustc-cfg={version_cfg}");
+        }
     }
 }