Introduce a typedef for the IDToValue type

git-svn-id: https://llvm.org/svn/llvm-project/polly/trunk@216843 91177308-0d34-0410-b5e6-96231b3b80d8
Fix formatting

git-svn-id: https://llvm.org/svn/llvm-project/polly/trunk@216844 91177308-0d34-0410-b5e6-96231b3b80d8