fail compilation if compiling outside of windows

src/main.rs

@@ -1,5 +1,8 @@
 #![cfg_attr(not(debug_assertions), windows_subsystem = "windows")]
 
+#[cfg(not(target_os = "windows"))]
+compile_error!("This application must be compiled on Windows.");
+
 mod features;
 mod gui;
 mod util;