Tests fail to link on arm32

[talex5]

This seems to be an OCaml bug: https://github.com/ocaml/ocaml/issues/10571

However, https://github.com/ocaml/ocaml/issues/10571#issuecomment-905938754 mentions a possible work-around:

The main reason why the frame needs to be enormous seems to be the coercion between the inferred type for the MakeRPC functor's body and the declared type in test.mli: all modules and submodules are coerced at the same point, so every single value defined in any of these modules has to be kept alive until the end. If you have some way to patch your code generator, you might want to add explicit coercions on every submodule you define in the implementation; this should decrease significantly the number of values that need to stay alive until the end.