[x86] In the new vector shuffle lowering, when trying to do another
layer of tie-breaking sorting, it really helps to check that you're in
a tie first. =] Otherwise the whole thing cycles infinitely. Test case
added, another one found through fuzz testing.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218523 91177308-0d34-0410-b5e6-96231b3b80d8