message: [mlir] Add Python binding libraries for more submodules
  In particular, Conversions and Transforms are built as separate dynamic
  libraries that can be imported by Python.
diff: @@ -445,7 +445,13 @@ cc_library(
  ],
  )
  -exports_files(["lib/Bindings/Python/MainModule.cpp"])
  +exports_files(
  + [
  + "lib/Bindings/Python/MainModule.cpp",
  + "lib/Bindings/Python/Conversions/Conversions.cpp",
  + "lib/Bindings/Python/Transforms/Transforms.cpp",
  + ],
  +)
  cc_library(
  name = "MLIRBindingsPythonCore",
  @@ -482,24 +488,58 @@ cc_library(
  ],
  )
  +PYBIND11_COPTS = [
  + "-fexceptions",
  + "-frtti",
  +]
  +
  +PYBIND11_FEATURES = [
  + # Cannot use header_modules (parse_headers feature fails).
  + "-use_header_modules",
  +]
  +
  # Dynamic library with the MLIR Python extension.
  cc_binary(
  name = "_mlir.so",
  srcs = ["lib/Bindings/Python/MainModule.cpp"],
  # These flags are needed for pybind11 to work.
  - copts = [
  - "-fexceptions",
  - "-frtti",
  - ],
  - features = [
  - # Cannot use header_modules (parse_headers feature fails).
  - "-use_header_modules",
  - ],
  + copts = PYBIND11_COPTS,
  + features = PYBIND11_FEATURES,
  linkshared = 1,
  linkstatic = 0,
  deps = [":MLIRBindingsPythonCore"],
  )
  +# Dynamlic library with the MLIR Conversions Python extension.
  +cc_binary(
  + name = "_mlirConversions.so",
  + srcs = ["lib/Bindings/Python/Conversions/Conversions.cpp"],
  + copts = PYBIND11_COPTS,
  + features = PYBIND11_FEATURES,
  + linkshared = 1,
  + linkstatic = 0,
  + deps = [
  + ":CAPIConversion",
  + "//third_party/pybind11",
  + "//third_party/python_runtime:headers",
  + ],
  +)
  +
  +# Dynamlic library with the MLIR Transforms Python extension.
  +cc_binary(
  + name = "_mlirTransforms.so",
  + srcs = ["lib/Bindings/Python/Transforms/Transforms.cpp"],
  + copts = PYBIND11_COPTS,
  + features = PYBIND11_FEATURES,
  + linkshared = 1,
  + linkstatic = 0,
  + deps = [
  + ":CAPITransforms",
  + "//third_party/pybind11",
  + "//third_party/python_runtime:headers",
  + ],
  +)
  +
  ##---------------------------------------------------------------------------##
  td_library(
  