[Polly][test] Test difference between isl::stat:ok() and isl::stat::error().

[Polly][test] Test difference between isl::stat:ok() and isl::stat::error().

The foreach callback wrappers tests check the return values of isl::stat:ok() and isl::stat::error() separately. However, due to the the container they are iterating over containing just one element, they are actually not testing the difference between them.

This patch changes to set to be iterated over to contain 2 element to make returning sl::stat:ok (continue iterating the next element) and isl::stat::error (break after current element) have different effects other than the return value of the foreach itself.

Reviewed By: patacca

Differential Revision: https://reviews.llvm.org/D107395