message: Use relative path for TableGen include with MLIR HLO
  Fix TensorFlow build when used as an external project.
diff: @@ -345,15 +345,17 @@ gentbl(
  tbl_outs = [("", "operator_writers.inc")],
  tblgen = ":operator_writer_gen",
  td_file = "//tensorflow/compiler/mlir/hlo:include/mlir-hlo/Dialect/mhlo/IR/hlo_ops.td",
  - # TODO(aminim): Figure out why td_relative_includes doesn't work here.
  - td_includes = [
  - "tensorflow/compiler/mlir/hlo/include",
  + td_relative_includes = [
  + "../hlo/include",
  ],
  td_srcs = [
  "@llvm-project//mlir:include/mlir/IR/OpBase.td",
  "@llvm-project//mlir:include/mlir/Interfaces/InferTypeOpInterface.td",
  "@llvm-project//mlir:include/mlir/Interfaces/SideEffectInterfaces.td",
  "//tensorflow/compiler/mlir/hlo:hlo_ops_td_files",
  + # Any file in this directory is OK: this will force the current path to exist so
  + # that the relative path can be resolved.
  + "BUILD",
  ],
  )
  