Have pom2mk list all duplicates modules

For easier debugging if there are multiple duplicates

Bug: 76692459
Test: ./update_current.py -x <build-id>

Change-Id: I3079cb4ed1cfd365d792a7b41c9cdb4e7a1e148f

cmd/pom2mk/pom2mk.go

@@ -360,6 +360,7 @@ The makefile is written to stdout, to be put in the current directory (often as
 
 	poms := []*Pom{}
 	modules := make(map[string]*Pom)
+	duplicate := false
 	for _, filename := range filenames {
 		pom, err := parse(filename)
 		if err != nil {
@@ -373,11 +374,15 @@ The makefile is written to stdout, to be put in the current directory (often as
 
 			if old, ok := modules[key]; ok {
 				fmt.Fprintln(os.Stderr, "Module", key, "defined twice:", old.PomFile, pom.PomFile)
+				duplicate = true
 			}
 
 			modules[key] = pom
 		}
 	}
+	if duplicate {
+		os.Exit(1)
+	}
 
 	for _, pom := range poms {
 		pom.FixDeps(modules)