MLIR materializes various enumeration-based LLVM IR operands as enumeration
attributes using ODS. This requires bidirectional conversion between different
but very similar enums, currently hardcoded. Extend the ODS modeling of
LLVM-specific enumeration attributes to include the name of the corresponding
enum in the LLVM C++ API as well as the names of specific enumerants. Use this
new information to automatically generate the conversion functions between enum
attributes and LLVM API enums in the two-way conversion between the LLVM
dialect and LLVM IR proper.
Use the generated conversion functions for Linkage attributes as an example.
We've have quite a few *Sym here. What about adding some documentation for them (potentially with a good example)?