[libstdc++] Different version tag for libsupc++, document , config option

[Phil Edwards]

> After I said "CXXABI" I realized the ABI doc specifies 'libcxa' for this 
> stuff.

Is this the ABI doc at codesourcery.com/cxx-abi/ ?  I need to read that
over again.  Among other things, I've always wondered what CXA stood for.


Phil

-- 
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