GNU: Correct C23 flags

Non-final forms aren't supported yet, unlike C++23.
Seems I might've gotten confused due to that when I added these.

Fixes #22453.

Modules/Compiler/GNU-C.cmake

@@ -42,8 +42,8 @@ if(CMAKE_C_COMPILER_VERSION VERSION_GREATER_EQUAL 8.1)
 endif()
 
 if(CMAKE_C_COMPILER_VERSION VERSION_GREATER_EQUAL 9.1)
-  set(CMAKE_C23_STANDARD_COMPILE_OPTION "-std=c23")
-  set(CMAKE_C23_EXTENSION_COMPILE_OPTION "-std=gnu23")
+  set(CMAKE_C23_STANDARD_COMPILE_OPTION "-std=c2x")
+  set(CMAKE_C23_EXTENSION_COMPILE_OPTION "-std=gnu2x")
 endif()
 
 __compiler_check_default_language_standard(C 3.4 90 5.0 11 8.1 17)