Merge topic 'cpp23_gcc' into release-3.20

9fbbebe3 GNU: C++23 support
c9a1e06a GNU: Final C++20 flags
05f8c817 GNU: C++17 default version

Acked-by: Kitware Robot <kwrobot@kitware.com>
Merge-request: !6108

Modules/Compiler/GNU-CXX.cmake

@@ -61,9 +61,14 @@ elseif (NOT CMAKE_CXX_COMPILER_VERSION VERSION_LESS 5.1)
   set(CMAKE_CXX17_EXTENSION_COMPILE_OPTION "-std=gnu++1z")
 endif()
 
-if (NOT CMAKE_CXX_COMPILER_VERSION VERSION_LESS 8.0)
+if(CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 11.1)
+  set(CMAKE_CXX20_STANDARD_COMPILE_OPTION "-std=c++20")
+  set(CMAKE_CXX20_EXTENSION_COMPILE_OPTION "-std=gnu++20")
+  set(CMAKE_CXX23_STANDARD_COMPILE_OPTION "-std=c++23")
+  set(CMAKE_CXX23_EXTENSION_COMPILE_OPTION "-std=gnu++23")
+elseif(CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 8.0)
   set(CMAKE_CXX20_STANDARD_COMPILE_OPTION "-std=c++2a")
   set(CMAKE_CXX20_EXTENSION_COMPILE_OPTION "-std=gnu++2a")
 endif()
 
-__compiler_check_default_language_standard(CXX 3.4 98 6.0 14)
+__compiler_check_default_language_standard(CXX 3.4 98 6.0 14 11.1 17)