rust: Change BinderBindings.h extension to .hpp

The build system now makes assumptions about how to interpret the
wrapper source for rust_bindgen modules. As BinderBindings.h is a C++
header, change it's extension to .hpp so the build system automatically
interprets it as a C++ header.

Bug: 163580541
Test: m libbinder_ndk_bindgen
Change-Id: I6ffd26b64ec388ec5a89b9138caeef37015ad973
diff --git a/libs/binder/rust/Android.bp b/libs/binder/rust/Android.bp
index 0234820..dc8270e 100644
--- a/libs/binder/rust/Android.bp
+++ b/libs/binder/rust/Android.bp
@@ -28,11 +28,8 @@
 rust_bindgen {
     name: "libbinder_ndk_bindgen",
     crate_name: "binder_ndk_bindgen",
-    wrapper_src: "sys/BinderBindings.h",
+    wrapper_src: "sys/BinderBindings.hpp",
     source_stem: "bindings",
-    cflags: [
-        "-x c++",
-    ],
     bindgen_flags: [
         // Unfortunately the only way to specify the rust_non_exhaustive enum
         // style for a type is to make it the default