In today's repo, attribute `llvm.emit_c_interface` of func op is handled
outside of `mlir::convertFuncOpToLLVMFuncOp` in `FuncOpConversion`
pattern. In some cases, `FuncOpConversion` can't be directly re-used,
but we still want to re-use the code to emit c interface for
`llvm.emit_c_interface`.
Changes in this PR
* move the code to generate c with "llvm.emit_c_interface" interface
into `mlir::convertFuncOpToLLVMFuncOp` to be able to re-use it.
* added unit test to verify c interface for jit can be generated
correctly if only call `convertFuncOpToLLVMFuncOp`.
* removed `FuncOpConversionBase`
---------
Co-authored-by: Fung Xie <ftse@nvidia.com>
a4490217fc