Disable the use of TBAA when using AA in CodeGen

There are currently two issues, of which I currently know, that prevent TBAA
from being correctly usable in CodeGen:

  1. Stack coloring does not update TBAA when merging allocas. This is easy
     enough to fix, but is not the largest problem.

  2. CGP inserts ptrtoint/inttoptr pairs when sinking address computations.
     Because BasicAA does not handle inttoptr, we'll often miss basic type punning
     idioms that we need to catch so we don't miscompile real-world code (like LLVM).

I don't yet have a small test case for this, but this fixes self hosting a
non-asserts build of LLVM on PPC64 when using -enable-aa-sched-mi and -misched=shuffle.