doc: -Wdelete-non-virtual-dtor supersedes -Wnon-virtual-dtor

The newer -Wdelete-non-virtual-dtor has no false positives and fewer
bugs. There is very little reason to use -Wnon-virtual-dtor instead.

gcc/ChangeLog:

	* doc/invoke.texi (C++ Dialect Options): Recommend using
	-Wdelete-non-virtual-dtor instead of -Wnon-virtual-dtor.
1 file changed