Use -polly-codegen-isl in isl-codegen test

Reported-by: Sebastian Pop <spop@codeaurora.org>

git-svn-id: https://llvm.org/svn/llvm-project/polly/trunk@201902 91177308-0d34-0410-b5e6-96231b3b80d8
Dependences: Do not assign 'WAW' twice

Reported-by: Sebastian Pop <spop@codeaurora.org>
Reported-by: Yabin Hu <yabin.hwu@gmail.com>

git-svn-id: https://llvm.org/svn/llvm-project/polly/trunk@201903 91177308-0d34-0410-b5e6-96231b3b80d8