Use cfg aliases throught the code base

Co-authored-by: Mads Marquart <mads@marquart.dk>

build.rs

@@ -0,0 +1,21 @@
+use cfg_aliases::cfg_aliases;
+
+fn main() {
+    // The script doesn't depend on our code
+    println!("cargo:rerun-if-changed=build.rs");
+    // Setup cfg aliases
+    cfg_aliases! {
+        // Systems.
+        android_platform: { target_os = "android" },
+        wasm_platform: { target_arch = "wasm32" },
+        macos_platform: { target_os = "macos" },
+        ios_platform: { target_os = "ios" },
+        windows_platform: { target_os = "windows" },
+        apple: { any(target_os = "ios", target_os = "macos") },
+        free_unix: { all(unix, not(apple), not(android_platform)) },
+
+        // Native displays.
+        x11_platform: { all(feature = "x11", free_unix, not(wasm)) },
+        wayland_platform: { all(feature = "wayland", free_unix, not(wasm)) },
+    }
+}