[CMake] selecting correct g++/libstdc++.so pair

[Russell L. Carter]

Hi all,
I have three g++ versions installed.  Debian's native g++-4.3 and
g++-4.4 both use /usr/lib/libstdc++.so.6.13, while
/usr/local/bin/g++-4.5 needs /usr/local/lib64/libstdc++.so.6.14.

If I use CXX=/usr/local/bin/g++-4.5 at configure time, executables
are linked against /usr/lib/libstdc++.so.6.13, which is not what
I want.  What is the approved Cmake Way for insuring that executables
using g++-4.5 link against libstdc++.so.6.14?

Thanks,
Russell