HWASAN: No DW_OP_LLVM_tag_offset with opt above -O0

[vitalybuka]

DW_OP_LLVM_tag_offset is present in -O0, but not -O1 https://godbolt.org/z/3dj6bzz4z

Reasons is AssignmentTrackingPass and -instcombine-lower-dbg-declare replace @llvm.dbg.declare with @llvm.dbg.assign but we don't attach DW_OP_LLVM_tag_offset to @llvm.dbg.assign.

[jmorse]

Had a quick chat with @OCHyams about this; all the trickyness with assignment-tracking likely comes from it having two DIExpressions, one for "How to compute the variables value" and the other "How to compute the stack location", presumably DW_OP_llvm_tag_offset wants to be applied to the latter. We'll give it a prod shortly.