DebugLocEntry: Restore the comparison predicate from before the
refactoring in 215384. This way it can unique multiple entries describing
the same piece even if they don't have the exact same location.
(The same piece may get merged in and be added from OpenRanges).
There ought to be a more elegant solution for this, though.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@215418 91177308-0d34-0410-b5e6-96231b3b80d8