This allows BBVectorize to check the "unknown instruction" list in the
alias sets. This is important to prevent instruction fusing from reordering
function calls. Resolves PR11920.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@150250 91177308-0d34-0410-b5e6-96231b3b80d8
