On Wayland, add support for fractional scaling

This adds support for the fractional scaling on Wayland via the
wp-fractional-scale protocol.

Co-authored-by: Julian Orth <ju.orth@gmail.com>

build.rs

@@ -1,8 +1,34 @@
 use cfg_aliases::cfg_aliases;
 
+#[cfg(all(
+    any(
+        target_os = "linux",
+        target_os = "dragonfly",
+        target_os = "freebsd",
+        target_os = "openbsd",
+        target_os = "netbsd",
+    ),
+    feature = "wayland",
+))]
+mod wayland {
+    use std::env;
+    use std::path::PathBuf;
+    use wayland_scanner::Side;
+
+    pub fn main() {
+        let mut path = PathBuf::from(env::var("OUT_DIR").unwrap());
+        path.push("fractional_scale_v1.rs");
+        wayland_scanner::generate_code(
+            "wayland_protocols/fractional-scale-v1.xml",
+            &path,
+            Side::Client,
+        );
+    }
+}
+
 fn main() {
     // The script doesn't depend on our code
-    println!("cargo:rerun-if-changed=build.rs");
+    println!("cargo:rerun-if-changed=build.rs:wayland_protocols");
     // Setup cfg aliases
     cfg_aliases! {
         // Systems.
@@ -20,4 +46,17 @@ fn main() {
         wayland_platform: { all(feature = "wayland", free_unix, not(wasm), not(redox)) },
         orbital_platform: { redox },
     }
+
+    // XXX aliases are not available for the build script itself.
+    #[cfg(all(
+        any(
+            target_os = "linux",
+            target_os = "dragonfly",
+            target_os = "freebsd",
+            target_os = "openbsd",
+            target_os = "netbsd",
+        ),
+        feature = "wayland",
+    ))]
+    wayland::main();
 }