libDebugInfo is for generating DWARF, Dwarf.h et al are just for the DWARF constants.
things like libIR don’t need to generate debug info, so they don’t depend on libDebugInfo - but they do use DWARF constants to encode debug info in the IR (the debug info metadata), so it’s useful to have it in Support instead of having to pull in the full libDebugInfo dependency.
We don't use CodeView constants to encode LLVM IR debug info. We translate
DWARF tags in the IR to the appropriate CV records and kinds.