Add a system test to check the mk and ninja files generated by incremental build.

Bug: 358428180
Test: Run the test locally.
Change-Id: If1862ee44976216f3c5a5c62d50c6d688d38023b

android/init.go

@@ -18,5 +18,6 @@ import "encoding/gob"
 
 func init() {
 	gob.Register(ModuleOutPath{})
+	gob.Register(PhonyPath{})
 	gob.Register(unstableInfo{})
 }