CodeGen: match up correct insertvalue indices when assessing tail calls.

When deciding whether a value comes from the aggregate or inserted value of an
insertvalue instruction, we compare the indices against those of the location
we're interested in. One of the lists needs reversing because the input data is
backwards (so that modifications take place at the end of the SmallVector), but
we were reversing both before leading to incorrect results.

Should fix PR23408

llvm-svn: 236457