c++-mode does not support C-h S?

[Sergey Organov]

Hello,

In a buffer with c++-mode major mode, pressing C-h S causes appearance
of the prompt "Use symbol help mode: " in the minibuffer that, according
to the manual, means c++-mode does not support info-lookup-symbol?:

 If you use C-h S in a major mode that does not support it, it asks you
 to specify the symbol help mode. You should enter a command such as
 c-mode that would select a major mode which C-h S does support.

How do I configure c++-mode to use c-mode to lookup symbols, and why
it's not configured this way by default?

Thanks,
-- Sergey Organov