Added checking code whehter target supports specific dag combining about rotate
or not. The corresponding dag patterns are as following:

"DAGCombier::MatchRotate" function in DAGCombiner.cpp
Pattern1
// fold (or (shl (*ext x), (*ext y)),
//          (srl (*ext x), (*ext (sub 32, y)))) ->
//   (*ext (rotl x, y))
// fold (or (shl (*ext x), (*ext y)),
//          (srl (*ext x), (*ext (sub 32, y)))) ->
//   (*ext (rotr x, (sub 32, y)))

pattern2
// fold (or (shl (*ext x), (*ext (sub 32, y))),
//          (srl (*ext x), (*ext y))) ->
//   (*ext (rotl x, y))
// fold (or (shl (*ext x), (*ext (sub 32, y))),
//          (srl (*ext x), (*ext y))) ->
//   (*ext (rotr x, (sub 32, y)))


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191905 91177308-0d34-0410-b5e6-96231b3b80d8