Where should my migration files be if the entity is in from a shared library?

I'm working on a project with shared entities in a library.
Assuming that 3 projects use these entities, where should I put my doctrine migration files ? In the library ? or in each project ? What's the best practice about that ?
I tried putting it them in the bundle but then I had to implement a VersionComparator to tell Doctrine which migration to run first.