Bump min cxx standard to 17

[oandreeva-nv]

Setting a min required cxx standard for Triton to 17.

Note in our containers default cxx is 17, thus no -std=.. flag is shown. However, if higher version is desired, the following command:

cmake -DTRITON_MIN_CXX_STANDARD=20 -DCMAKE_INSTALL_PREFIX:PATH=`pwd`/install .. && make -j1 VERBOSE=1 install

will add -std=gnu++20 flag during build.

This PR:

• adds TRITON_MIN_CXX_STANDARD cmake variable, which defaults to 17
• uses the above variable to specify cxx standard in target_compile_features(... PRIVATE cxx_std_${TRITON_MIN_CXX_STANDARD}), to avoid hardcoded values

This way to recompile Triton in higher standard, one can simply specify -DTRITON_MIN_CXX_STANDARD=20 option for cmake command, as shown above.

Related PRs:

• core: Bump min cxx standard to 17 core#303
• common: Bump min cxx standard to 17 common#110
• backend: Bump min cxx standard to 17 backend#92
• third-party: Bump min cxx standard to 17 third_party#50
• client: Bump min cxx standard to 17 client#450 [will keep as a draft for now per @debermudez request regarding PA]
• checksum_repository_agent: Bump min required cxx standard to 17 checksum_repository_agent#9

Backends:

• openvino_backend: Bumping min required cxx standard to 17 openvino_backend#61
• python_backend: Bumping min required cxx standard to 17 python_backend#332
• pytorch_backend: Bumping min required cxx standard to 17 pytorch_backend#122
• tensorrt_backend : Bumping min required cxx standard to 17 tensorrt_backend#79
• tensorflow_backend: Bumping min required cxx standard to 17 tensorflow_backend#100
• onnxruntime_backend: Bumping min required cxx standard to 17 onnxruntime_backend#230
• square_backend: Bumping min required cxx standard to 17 square_backend#15
• repeat_backend: Bumping min required cxx standard to 17 repeat_backend#10
• identity_backend: Bumping min required cxx standard to 17 identity_backend#27

Note:
tensorrt_llm_backend and local_cache are already have c++17 standard, redis cache has c++20 standard specified, so these repos can be updated separately