Implications of tighter integration of libg++

[Joe Buck]

>   > It is desirable to place libraries compiled against and dependent upon
>   > a given version of g++, and their related header files, into the
>   > compiler's lib and include directory.

Yes, but once we have complete standards conformance, we should get to the
point where libstdc++ always has the exact same API, so this kind of
dependency doesn't really exist.  I think that the compiler-specific
lib directory really makes sense only for static libraries, not shared
libraries.