Do not force the C++ standard to 17, if it is already set by an including project or developer

Signed-off-by: Rickert, Jonas <[email protected]>

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)
+set(CMAKE_CXX_STANDARD 17 CACHE STRING "C++ standard to use")
 
 set(CMAKE_EXPORT_COMPILE_COMMANDS ON)