build: Update C++ standard from c++17 to c++20 (#455) (#456)

Upstream PyTorch raised ATen's minimum required C++ standard from 17
to 20 (pytorch/pytorch#178150), which broke the pytorch_backend build.
Align this repo's TRITON_MIN_CXX_STANDARD/CMAKE_CXX_STANDARD default
with that floor for consistency across the stack.

TRI-1877

(cherry picked from commit 26764b9)

Author: mc-nv

CMakeLists.txt

@@ -28,8 +28,8 @@ cmake_minimum_required(VERSION 3.31.8)
 
 project(tritonpythonbackend LANGUAGES C CXX)
 
-# Use C++17 standard as Triton's minimum required.
-set(TRITON_MIN_CXX_STANDARD 17 CACHE STRING "The minimum C++ standard which features are requested to build this target.")
+# Use C++20 standard as Triton's minimum required.
+set(TRITON_MIN_CXX_STANDARD 20 CACHE STRING "The minimum C++ standard which features are requested to build this target.")
 
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