Enable genrule modules for Rust host binaries

* Add HostToolPath to use rust_binary_host modules as host tools.

Bug: 157666974
Test: make with local genrule examples
Change-Id: I9648313c0f0695d2e695f18ded4710350b2d6475
diff --git a/rust/rust.go b/rust/rust.go
index 03efb75..6c60348 100644
--- a/rust/rust.go
+++ b/rust/rust.go
@@ -886,6 +886,18 @@
 	return name
 }
 
+var _ android.HostToolProvider = (*Module)(nil)
+
+func (mod *Module) HostToolPath() android.OptionalPath {
+	if !mod.Host() {
+		return android.OptionalPath{}
+	}
+	if _, ok := mod.compiler.(*binaryDecorator); ok {
+		return mod.outputFile
+	}
+	return android.OptionalPath{}
+}
+
 var Bool = proptools.Bool
 var BoolDefault = proptools.BoolDefault
 var String = proptools.String