Add dependency to existing Android.mk files

So that we generate the Android.mk file if it is removed. Adding
Android.mk files is already handled by the implicit dependencies in
common.Glob

Change-Id: I568e24b7bc44ecadbbe01c1f7c6a97afd819c7db

common/module.go

@@ -588,6 +588,9 @@ func (c *buildTargetSingleton) GenerateBuildActions(ctx blueprint.SingletonConte
 
 		// Existing Android.mk file, use that instead
 		if len(files) > 0 {
+			for _, file := range files {
+				ctx.AddNinjaFileDeps(file)
+			}
 			continue
 		}