Lift the speculation visitor above all the helpers that are targeted at

Lift the speculation visitor above all the helpers that are targeted at
the rewrite visitor to make the fact that the speculation is completely
independent a bit more clear.

I promise that this is just a cut/paste of the one visitor and adding
the annonymous namespace wrappings. The diff may look completely
preposterous, it does in git for some reason.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@165284 91177308-0d34-0410-b5e6-96231b3b80d8