/// getOrCreateDebugLocID - Look up the DebugLocTuple index with the given
/// source file, line, and column. If none currently exists, create a new
/// DebugLocTuple, and insert it into the DebugIdMap.
/// getOrCreateDebugLocID - Look up the DebugLocTuple index with the given
/// source file, line, and column. If none currently exists, create a new
/// DebugLocTuple, and insert it into the DebugIdMap.