Declare PostDominatorTree as a class

Before it was declared at a struct, which differs from
DominatorTree. Make it a class so both can be declared
the same way without hitting the warning about mismatched
struct vs. class declarations.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@324760 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed