Merge pull request #451 from Xilinx/jrickert.do_not_set_cache_variable

Set CMAKE_CXX_STANDARD to 20 to allow building with newer protobuf versions.

Author: jorickert

CMakeLists.txt

@@ -22,7 +22,7 @@ if (NOT ONNX_MLIR_ENABLE_PYBIND)
   set(ONNX_MLIR_INSTALL_PYTHON_EXTENSIONS OFF)
 endif()
 
-set(CMAKE_CXX_STANDARD 17 CACHE STRING "C++ standard to use")
+set(CMAKE_CXX_STANDARD 20)
 
 set(CMAKE_EXPORT_COMPILE_COMMANDS ON)