Change build.rs to use the older : rather than ::

This allows supporting Rust < 1.77.

Author: tgross35

libm/build.rs

@@ -2,10 +2,10 @@ use std::env;
 
 fn main() {
     println!("cargo:rerun-if-changed=build.rs");
-    println!("cargo::rustc-check-cfg=cfg(assert_no_panic)");
-    println!("cargo::rustc-check-cfg=cfg(feature, values(\"unstable\"))");
+    println!("cargo:rustc-check-cfg=cfg(assert_no_panic)");
+    println!("cargo:rustc-check-cfg=cfg(feature, values(\"unstable\"))");
 
-    println!("cargo::rustc-check-cfg=cfg(feature, values(\"checked\"))");
+    println!("cargo:rustc-check-cfg=cfg(feature, values(\"checked\"))");
 
     #[allow(unexpected_cfgs)]
     if !cfg!(feature = "checked") {