Remove the dependency on a homebrew version of MemorySSA/Andersen
LLVM has an implementation of Andersen's alias analysis and also an implementation of MemorySSA.
I took a quick look at their implementation and their API differs significantly from how we use our own MemorySSA/AA passes.
It would be a (very?) long task, but I think it's a sound goal to rather depend on the maintained versions of these passes in LLVM.
I should document more this issue once I have a more accurate understanding of how PARCOACH uses these analysis.