Add mlir out of tree build

[jackalcooper]

No description provided.

[jackalcooper]

hi @sylvestre. It has been reproduced in the latest commit

--
Command Output (stderr):
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CMake Error at /usr/lib/llvm-15/lib/cmake/mlir/AddMLIR.cmake:[283](https://github.com/opencollab/llvm-toolchain-integration-test-suite/runs/6108847481?check_suite_focus=true#step:6:283) (message):
  Cannot build aggregate from imported targets which were not installed via
  MLIR_INSTALL_AGGREGATE_OBJECTS (for MLIRCAPIIR).
Call Stack (most recent call first):
  mlir_dialect/cylib/MLIR/CMakeLists.txt:49 (add_mlir_aggregate)


CMake Error at /usr/lib/llvm-15/lib/cmake/mlir/AddMLIR.cmake:283 (message):
  Cannot build aggregate from imported targets which were not installed via
  MLIR_INSTALL_AGGREGATE_OBJECTS (for MLIRCAPIRegistration).
Call Stack (most recent call first):
  mlir_dialect/cylib/MLIR/CMakeLists.txt:49 (add_mlir_aggregate)

[sylvestre]

25 files changed, can you please reduce it? it is way big, sorry :(

[jackalcooper]

25 files changed, can you please reduce it? it is way big, sorry :(

the cpp code are removed now.