Correctly handle multiple DBG_VALUE instructions at the same SlotIndex.

It is possible to have multiple DBG_VALUEs for the same variable:

32L TEST32rr %vreg0<kill>, %vreg0, %EFLAGS<imp-def>; GR32:%vreg0
    DBG_VALUE 2, 0, !"i"
    DBG_VALUE %noreg, %0, !"i"

When that happens, keep the last one instead of the first.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@136842 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed