[PM/AA] Extract the ModRef enums from the AliasAnalysis class in

[PM/AA] Extract the ModRef enums from the AliasAnalysis class in
preparation for de-coupling the AA implementations.

In order to do this, they had to become fake-scoped using the
traditional LLVM pattern of a leading initialism. These can't be actual
scoped enumerations because they're bitfields and thus inherently we use
them as integers.

I've also renamed the behavior enums that are specific to reasoning
about the mod/ref behavior of functions when called. This makes it more
clear that they have a very narrow domain of applicability.

I think there is a significantly cleaner API for all of this, but
I don't want to try to do really substantive changes for now, I just
want to refactor the things away from analysis groups so I'm preserving
the exact original design and just cleaning up the names, style, and
lifting out of the class.

Differential Revision: http://reviews.llvm.org/D10564

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@242963 91177308-0d34-0410-b5e6-96231b3b80d8