Lumen 12.0.0-dev (2020-08-04)

Contains a large backlog of changes to LLVM and MLIR. Of note, improvements to MLIR have added additional expressiveness to the definition of operations (to allow for properly defining optional arguments), type/attribute traits, test case reduction, and a variety of other miscellaneous changes.

For Lumen, this is primarily a release to keep us in parity with upstream, though we have taken advantage of some of the TableGen improvements to clean up our definition of some operations.