[CLANG][DWARF] Handle DIE offset collision in DW_IDX_parent (#95039)

This fixes https://github.com/llvm/llvm-project/issues/93886. The UnitID
is not
unique between CUs and TUs. This led to DW_IDX_parent to point ot an
entry for a
DIE in a CU if it had the same relative offset as a TU die.

Added a IsTU to the hash for parent chain.