only use swift_rs on macOS in build script

missed this in #239, silly me

apps/desktop/src-tauri/build.rs

@@ -1,8 +1,11 @@
-use swift_rs::build::{link_swift, link_swift_package};
-
 fn main() {
-	link_swift();
-	link_swift_package("sd-desktop-macos", "./native/macos/");
+	#[cfg(target_os = "macos")]
+	{
+		use swift_rs::build::{link_swift, link_swift_package};
+
+		link_swift();
+		link_swift_package("sd-desktop-macos", "./native/macos/");
+	}
 
 	tauri_build::build();
 }