chore: checkpoint before Python removal

vendor/libm/build.rs

@@ -0,0 +1,18 @@
+use std::env;
+
+mod configure;
+
+fn main() {
+    let cfg = configure::Config::from_env();
+
+    println!("cargo:rerun-if-changed=build.rs");
+    println!("cargo:rerun-if-changed=configure.rs");
+    println!("cargo:rustc-check-cfg=cfg(assert_no_panic)");
+
+    // If set, enable `no-panic`. Requires LTO (`release-opt` profile).
+    if env::var("ENSURE_NO_PANIC").is_ok() {
+        println!("cargo:rustc-cfg=assert_no_panic");
+    }
+
+    configure::emit_libm_config(&cfg);
+}