GLIBCXX_3.4.9 not found
I know this is a very old question, but ...
It's not usually a good idea to replace the system compiler (i.e. the one in /usr) because the entire system will have been built with it and depend on it.
It's usually better to install the new compiler to a separate location and then see the libstdc++ FAQ How do I insure that the dynamically linked library will be found? and Finding Dynamic or Shared Libraries in the manual for how to ensure the correct libstdc++.so is found at runtime.
The other answers here should be fine, but the 'quick and easy' solution if you do happen to have gcc installed to /usr/local/ is to just add the new libs to the LD_LIBRARY_PATH
export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/usr/local/lib64
You can also check the to see if you have the right versions of GLIBC installed using
strings /usr/lib/libstdc++.so.6 | grep GLIBC
strings /usr/local/lib64/libstdc++.so.18 | grep GLIBC
I got this last tip from another forum so credits due where credits due!
The problem is that you built your new GCC incorrectly: on Linux you should use
./configure --prefix=/usr
The default installation prefix is /usr/local, which is why make install put gcc and g++ binaries into /usr/local/bin, etc.
What's happening to you now is that you compile and link using the new (symlinked) GCC 4.2.4, but at runtime your program binds to the old /usr/lib64/libstdc++.so.6 (version 6.0.8, instead of required 6.0.9). You can confirm that by running ldd build/ALPHA_SE/m5.opt: you should see that it uses /usr/lib64/libstdc++.so.6.
There are several fixes you could do.
env LD_LIBRARY_PATH=/usr/local/lib64 ldd build/ALPHA_SE/m5.opt
should show you that setting LD_LIBRARY_PATH is sufficient to redirect the binary to correct library, and
LD_LIBRARY_PATH=/usr/local/lib64 build/ALPHA_SE/m5.opt
should just run. You could "bake" this path into m5.opt binary by relinking it with -Wl,-rpath=/usr/local/lib64.
A more permanent solution is to fix the libraries the same way you fixed the binaries:
cd /usr/lib64 && mv libstdc++.so.6 libstdc++.so.6_bak &&
ln -s /usr/local/lib64/libstdc++.so.6 .
An even better solution is to reconfigure the new GCC with --prefix=/usr, and then make all install.