Compute the correct jump table entries on 32 bit windows.

On 32 bit windows we use label differences and .set does not suppress
rolocations, a combination that was not used before r220256.

This fixes PR21497.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221456 91177308-0d34-0410-b5e6-96231b3b80d8