[libstdc++] Make use of runtime demangler

[Phil Edwards]

rth approved the libiberty changes in private email, so I have now checked
in the patches to trunk and branch.

Now that /a/ demangler is in place to be used, we can work on /which/
demangler it's going to be.  :-)


Phil

-- 
If ye love wealth greater than liberty, the tranquility of servitude greater
than the animating contest for freedom, go home and leave us in peace.  We seek
not your counsel, nor your arms.  Crouch down and lick the hand that feeds you;
and may posterity forget that ye were our countrymen.            - Samuel Adams