Revert commits r222146 and r222137.

They were producing the wrong result if NumBits == BitsInWord. The old mask
produced -1, the new mask 0.

This should fix the 32 bit bots.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222166 91177308-0d34-0410-b5e6-96231b3b80d8