Added -Wsuggest-override to the warning list

This warning is available on GCC since 5.1 and Clang since 11.0.0.

Since GCC 9.2 it also does not warn if 'final' is used instead of
'override'. This was the case in Clang since the warning was introduced.

cmake/CompilerWarnings.cmake

@@ -56,6 +56,7 @@ function(
         -Wdouble-promotion # warn if float is implicit promoted to double
         -Wformat=2 # warn on security issues around functions that format output (ie printf)
         -Wimplicit-fallthrough # warn on statements that fallthrough without an explicit annotation
+        -Wsuggest-override # warn if an overridden member function is not marked 'override' or 'final'
     )
   endif()