Move tests that depend on -stats under 'requires asserts'

This fixes issues caused by the following commit:

  r176733 | jvoung | 2013-03-08 17:56:31 -0500
  Disable statistics on Release builds and move tests that depend on -stats.

Reported by: Jack Howarth <howarth@bromo.med.uc.edu>

git-svn-id: https://llvm.org/svn/llvm-project/polly/trunk@176856 91177308-0d34-0410-b5e6-96231b3b80d8