GNU: C++23 support

Added in GCC commit 78739c2df788ee5c868d998a6333d453317d8711, released in 11.1.
No lettered variant beforehand this time around.

Implements #22139.

Modules/Compiler/GNU-CXX.cmake

@@ -64,6 +64,8 @@ endif()
 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")