as it causes a layering violation/dependency cycle:
llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp -> llvm/DebugInfo/DWARF/DWARFExpression.h
llvm/include/llvm/DebugInfo/DWARF/DWARFOptimizer.h -> llvm/CodeGen/NonRelocatableStringpool.h
This reverts commit abc7f6800df8a1f40e1e2c9ccce826abb0208284.