MSVC: Tolerate c_std_17 and c_std_23 features on older compiler versions

MSVC `cl` versions prior to 19.27 had no `-std:c*` flags for C
standards.  List the `c_std_{17,23}` features anyway.  This allows
projects to at least attempt compilation with these compilers since they
do not have any modes.

Modules/Compiler/MSVC-C.cmake

@@ -49,6 +49,8 @@ else()
       c_std_90
       c_std_99
       c_std_11
+      c_std_17
+      c_std_23
       c_function_prototypes
       )
     list(APPEND CMAKE_C90_COMPILE_FEATURES c_std_90 c_function_prototypes)