Fix linked objctive-C symbols on old macOS versions

build.rs

@@ -1,11 +1,29 @@
 extern crate cc;
+use std::env;
+
+const DEPLOYMENT_TARGET_VAR: &str = "MACOSX_DEPLOYMENT_TARGET";
 
 fn main() {
     if cfg!(target_os = "macos") {
+        let min_version = match env::var(DEPLOYMENT_TARGET_VAR) {
+            Ok(ver) => ver,
+            Err(_) => String::from(match env::var("CARGO_CFG_TARGET_ARCH").unwrap().as_str() {
+                "x86_64" => "10.8", // NSUserNotificationCenter first showed up here.
+                "aarch64" => "11.0", // Apple silicon started here.
+                arch => panic!("unknown arch: {}", arch),
+            }),
+        };
+
         cc::Build::new()
             .file("objc/notify.m")
             .flag("-fmodules")
-            .warnings(false)
+            .flag("-Wno-deprecated-declarations")
+            // `cc` doesn't try to pick up on this automatically, but `clang` needs it to
+            // generate a "correct" Objective-C symbol table which better matches XCode.
+            // See https://github.com/h4llow3En/mac-notification-sys/issues/45.
+            .flag(&format!("-mmacos-version-min={}", min_version))
             .compile("notify");
+
+        println!("cargo:rerun-if-env-changed={}", DEPLOYMENT_TARGET_VAR);
     }
 }