rust: Make binder-ndk-sys crate buildable via Cargo for NDK

Test: cargo build --target=aarch64-linux-android
Bug: 368303574
Change-Id: I58e41d34bc16d28bb899dc8a58dce12627f7ab4e
diff --git a/libs/binder/rust/Android.bp b/libs/binder/rust/Android.bp
index 4545d7b..19df972 100644
--- a/libs/binder/rust/Android.bp
+++ b/libs/binder/rust/Android.bp
@@ -140,6 +140,9 @@
         "--raw-line",
         "use libc::sockaddr;",
     ],
+    cflags: [
+        "-DANDROID_PLATFORM",
+    ],
     shared_libs: [
         "libbinder_ndk",
     ],
@@ -180,6 +183,9 @@
         // rustified
         "libbinder_ndk_bindgen_flags.txt",
     ],
+    cflags: [
+        "-DANDROID_PLATFORM",
+    ],
     shared_libs: [
         "libbinder_ndk_on_trusty_mock",
         "libc++",