[cleanup] Update Polly for moved header in LLVM r199082.


git-svn-id: https://llvm.org/svn/llvm-project/polly/trunk@199088 91177308-0d34-0410-b5e6-96231b3b80d8
Adapt to DomTree changes in r199104

git-svn-id: https://llvm.org/svn/llvm-project/polly/trunk@199157 91177308-0d34-0410-b5e6-96231b3b80d8
llvm/IR/Writer.h has been removed in llvm commit r198836 and seems useless in polly

git-svn-id: https://llvm.org/svn/llvm-project/polly/trunk@199360 91177308-0d34-0410-b5e6-96231b3b80d8