PGO branch weight: update edge weights in SelectionDAGBuilder.

When converting from "or + br" to two branches, or converting from
"and + br" to two branches, we correctly update the edge weights of
the two branches.

The previous attempt at r200431 was reverted at r200434 because of
two testing case failures. I modified my patch a little, but forgot
to re-run "make check-all".

Testing case CodeGen/ARM/lsr-unfolded-offset.ll is updated because of
the patch's impact on branch probability which causes changes in
spill placement.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@200502 91177308-0d34-0410-b5e6-96231b3b80d8