Modify test cases to work with SCEV based code generation

This patch includes tests where we actually need to adjust the CHECK lines
for SCEV based code generation. Besides these adjustments we add explicit
calls to -polly-codegen-scev=[true|false] and make sure we test both cases.

git-svn-id: https://llvm.org/svn/llvm-project/polly/trunk@222112 91177308-0d34-0410-b5e6-96231b3b80d8