Use the Cargo.toml version of the check-cfg squelching

It doesn't make older version of cargo complain.

https://doc.rust-lang.org/nightly/rustc/check-cfg/cargo-specifics.html#check-cfg-in-lintsrust-table

Fixes #576

Cargo.toml

@@ -83,3 +83,7 @@ required-features = ["static-curl", "ssl"]
 name = "multi-dl"
 path = "examples/multi-dl.rs"
 required-features = ["ssl"]
+
+[lints.rust.unexpected_cfgs]
+level = "warn"
+check-cfg = ["cfg(need_openssl_init, need_openssl_probe)"]

build.rs

@@ -1,12 +1,6 @@
 use std::env;
 
 fn main() {
-    println!(
-        "cargo::rustc-check-cfg=cfg(\
-            need_openssl_init,\
-            need_openssl_probe,\
-        )"
-    );
     // OpenSSL >= 1.1.0 can be initialized concurrently and is initialized correctly by libcurl.
     // <= 1.0.2 need locking callbacks, which are provided by openssl_sys::init().
     let use_openssl = match env::var("DEP_OPENSSL_VERSION_NUMBER") {

curl-sys/Cargo.toml

@@ -55,3 +55,7 @@ zlib-ng-compat = ["libz-sys/zlib-ng", "static-curl"]
 upkeep_7_62_0 = []
 poll_7_68_0 = []
 ntlm = []
+
+[lints.rust.unexpected_cfgs]
+level = "warn"
+check-cfg = ["cfg(libcurl_vendored,link_libnghttp2,link_libz,link_openssl)"]

curl-sys/build.rs

@@ -5,14 +5,6 @@ use std::process::Command;
 
 fn main() {
     println!("cargo:rerun-if-changed=curl");
-    println!(
-        "cargo::rustc-check-cfg=cfg(\
-            libcurl_vendored,\
-            link_libnghttp2,\
-            link_libz,\
-            link_openssl,\
-        )"
-    );
     let target = env::var("TARGET").unwrap();
     let windows = target.contains("windows");