rust: Bind to NDK subset of libbinder

Test: cargo build --target aarch64-linux-android
Bug: 368303574
Change-Id: Id4db842d5dff195393e1ce563479c58b91e3e879
diff --git a/libs/binder/rust/build.rs b/libs/binder/rust/build.rs
new file mode 100644
index 0000000..f3e6b53
--- /dev/null
+++ b/libs/binder/rust/build.rs
@@ -0,0 +1,4 @@
+fn main() {
+    // Anything with cargo is NDK only. If you want to access anything else, use Soong.
+    println!("cargo::rustc-cfg=android_ndk");
+}