[DebugInfo] Fix LineTest byteswap for cross-targeting builds

Summary:
The byte swap fix for big endian hosts in 9782c922 (for D81570)
swaps based on the host endianess,  but for cross-targeting builds (i.e.
big endian host targeting little endian) the host-endianess won't
necessarily match the generated DWARF. This change updates the test
to use symmetrical constants so the results aren't endian dependent.

Reviewers: jhenderson, hubert.reinterpretcast, stevewan, ikudrin

Reviewed By: ikudrin

Subscribers: ikudrin, aprantl, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D82827