[v3] more sophisticated versioning checks, enable by default

[Loren James Rittle]

In article <200202212339.g1LNdoV14149@fillmore.constant.com>,
Benjamin Kosnik <bkoz@redhat.com> writes:

> I think this makes this --enable flag consistent with other
> libstdc++-v3 configure flags, allows some systems to immediately start
> using symbol versioning without disrupting other systems, and at the
> same time allows a configuration option so that Loren can purposefully
> build a broken libstdc++ configuration on BSD to work through
> configuration issues. Does this seem fair, and a good way to proceed?

> Also, this enable flag should probably be documented on configopts.html.

A very fair and good way to proceed.  Great work Phil and Ben.

Regards,
Loren