Debug Info: Move the sorting and uniqueing of pieces from emitLocPieces()
into buildLocationList(). By keeping the list of Values sorted,
DebugLocEntry::Merge can also merge multi-piece entries.
Debug info: Further simplify the implementation of buildLocationList by
getting rid of the redundant DIVariable in the OpenRanges pair.
Debug info: Modify DebugLocEntry::addValue to take multiple values so it
only has to sort/unique values once per batch.
Debug info: Remove an obsolete constructor from DebugLocEntry.