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
[SimplifyCFG] Make the value type of the hole check bitmask a power-of-2.

When converting a switch to a lookup table we might have to generate a bitmaks
to encode and check for holes in the original switch statement.

The type of this mask depends on the number of switch statements, which can
result in illegal types for pretty much all architectures.

To avoid unnecessary type legalization and help FastISel this commit increases
the size of the bitmask to next power-of-2 value when necessary.

This fixes rdar://problem/18984639.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222168 91177308-0d34-0410-b5e6-96231b3b80d8