Lower llvm.expect intrinsic correctly for i1

LowerExpectIntrinsic previously only understood the idiom of an expect
intrinsic followed by a comparison with zero. For llvm.expect.i1, the
comparison would be stripped by the early-cse pass.

Patch by Daniel Micay.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@200664 91177308-0d34-0410-b5e6-96231b3b80d8