If the false case is the current basic block, then this is a self loop.

If the false case is the current basic block, then this is a self loop.
We do not want to emit "Loop: ... brcond Out; br Loop", as it adds an extra
instruction in the loop.  Instead, invert the condition and emit
"Loop: ... br!cond Loop; br Out.

Generalize the fix by moving it from PPCDAGToDAGISel to SelectionDAGLowering.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@26231 91177308-0d34-0410-b5e6-96231b3b80d8