Fix shl to produce the correct result when the bitwidth is > 64 and the

Fix shl to produce the correct result when the bitwidth is > 64 and the
shift amount is 0. Previously this code would do a lshr by the bit width
which can lead to incorrect results.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@37010 91177308-0d34-0410-b5e6-96231b3b80d8