update to std c++ 20

Author: 俞子丰

CMakeLists_crosscompile.txt

@@ -20,9 +20,9 @@ include(CheckPythonModuleExists)
 
 check_python_module_exists(PYTHON_HAVE_MARKUPSAFE markupsafe)
 
-# Stick to std c++17 for some code (std::unique_ptr to fwd-decl type) can not be compiled under c++23 after llvm upgrade
+# Stick to std c++20 for some code (std::unique_ptr to fwd-decl type) can not be compiled under c++23 after llvm upgrade
 # if (NOT CMAKE_CXX_STANDARD)
-set(CMAKE_CXX_STANDARD 17)
+set(CMAKE_CXX_STANDARD 20)
 # endif()
 
 if (NOT CMAKE_C_STANDARD)

CMakeLists_default.txt

@@ -20,9 +20,9 @@ include(CheckPythonModuleExists)
 
 check_python_module_exists(PYTHON_HAVE_MARKUPSAFE markupsafe)
 
-# Stick to std c++17 for some code (std::unique_ptr to fwd-decl type) can not be compiled under c++23 after llvm upgrade
+# Stick to std c++20 for some code (std::unique_ptr to fwd-decl type) can not be compiled under c++23 after llvm upgrade
 # if (NOT CMAKE_CXX_STANDARD)
-set(CMAKE_CXX_STANDARD 17)
+set(CMAKE_CXX_STANDARD 20)
 # endif()
 
 if (NOT CMAKE_C_STANDARD)