Codegeneration: Free memory correctly when using -polly-vectorizer=polly

This fixes PR19421.

Reported-by: Jeremy Huddleston Sequoia <jeremyhu@apple.com>

git-svn-id: https://llvm.org/svn/llvm-project/polly/trunk@206156 91177308-0d34-0410-b5e6-96231b3b80d8