Add a rust_bindgen_host module type.

Bug: 161826371
Test: Local rust_bindgen_host only provides host variants.
Change-Id: I8cc7819a193a6eefe40402e4b6a82f436c5de78a
diff --git a/rust/bindgen.go b/rust/bindgen.go
index 859223a..d377dad 100644
--- a/rust/bindgen.go
+++ b/rust/bindgen.go
@@ -48,6 +48,7 @@
 
 func init() {
 	android.RegisterModuleType("rust_bindgen", RustBindgenFactory)
+	android.RegisterModuleType("rust_bindgen_host", RustBindgenHostFactory)
 }
 
 var _ SourceProvider = (*bindgenDecorator)(nil)
@@ -152,6 +153,11 @@
 	return module.Init()
 }
 
+func RustBindgenHostFactory() android.Module {
+	module, _ := NewRustBindgen(android.HostSupported)
+	return module.Init()
+}
+
 func NewRustBindgen(hod android.HostOrDeviceSupported) (*Module, *bindgenDecorator) {
 	module := newModule(hod, android.MultilibBoth)