c++: -Wdeprecated enables later standard deprecations

By default -Wdeprecated warns about deprecations in the active standard.
When specified explicitly, let's also warn about deprecations in later
standards.

gcc/c-family/ChangeLog:

	* c-opts.cc (c_common_post_options): Explicit -Wdeprecated enables
	deprecations from later standards.

gcc/ChangeLog:

	* doc/invoke.texi: Explicit -Wdeprecated enables more warnings.