[PM] Refactor the analysis registration and pass pipeline parsing to

[PM] Refactor the analysis registration and pass pipeline parsing to
live in a class.

While this isn't really significant right now, I need to expose some
state to the pass construction expressions, and making them get
evaluated within a class context is a nice way to collect members that
they may need to access.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@227715 91177308-0d34-0410-b5e6-96231b3b80d8