[mlir] Don't make the ROCm conversions depend on the execution engine

[krzysz00]

Summary

During a conversion to MLIR_ENABLE_EXECUTION_ENGINE from checking for
the native target, the ROCm conversion passes (--serialize-to-hsaco)
were mistakenly flagged for being disabled if the execution ending is
not being built.

These passes use LLVM to build binaries for AMD GPUs, and so require
that backend to be enabled. However, they do not produce native code,
nor do they interact with the JIT or any of the execution engine
support libraries.

When building MLIR into a compiler library that's intended to produce
GPU binaries, we want to build only the AMDGPU backend and have the
binary serialization passes available. This change makes that
possible.

It looks like the CUDA path might currently require a native target,
it's hard to tell, so this commit leaves that if statement untouched.

[fmorac]

It looks good to me.

I think that condition was imposed at a time were OptUtils was a part of the ExecutionEngine lib see this comment:
https://github.com/llvm/llvm-project/blob/main/mlir/lib/ExecutionEngine/CMakeLists.txt#L17

Because it doesn't look like the serialization passes are dependent on the ExecutionEngine lib:
https://github.com/llvm/llvm-project/blob/main/mlir/lib/Dialect/GPU/CMakeLists.txt

mlir/CMakeLists.txt

 else()
   set(MLIR_ENABLE_CUDA_CONVERSIONS 0)
 endif()
 # TODO: we should use a config.h file like LLVM does
 add_definitions(-DMLIR_CUDA_CONVERSIONS_ENABLED=${MLIR_ENABLE_CUDA_CONVERSIONS})
 
 # Build the ROCm conversions and run according tests if the AMDGPU backend
 # is available.
-if ("AMDGPU" IN_LIST LLVM_TARGETS_TO_BUILD AND MLIR_ENABLE_EXECUTION_ENGINE)
+if ("AMDGPU" IN_LIST LLVM_TARGETS_TO_BUILD)
   set(MLIR_ENABLE_ROCM_CONVERSIONS 1)
 else()
   set(MLIR_ENABLE_ROCM_CONVERSIONS 0)
 endif()
 add_definitions(-DMLIR_ROCM_CONVERSIONS_ENABLED=${MLIR_ENABLE_ROCM_CONVERSIONS})
 
 set(MLIR_ENABLE_CUDA_RUNNER 0 CACHE BOOL "Enable building the mlir CUDA runner")
 set(MLIR_ENABLE_ROCM_RUNNER 0 CACHE BOOL "Enable building the mlir ROCm runner")