Revert "Revert "Update Polly for the removal of PreserveNames from IRBuilder stuff""

This reverts commit r263322 and reapplies r263296. The original
r263258 was reapplied in LLVM after being reverted in r263321 due to
issues with Release testing in Clang.

From: Mehdi Amini <mehdi.amini@apple.com>
llvm-svn: 263399