I had the same situation when porting the dedicated server of Zombie Panic! Source 3.0 (Source 2013) to Linux.
I don't remember if it's gonna 100% identical with HLDS/SteamCMD so I will explain what I did with ZPS 3.0 which is on Source 2013. Basically, you open the shell script that act as launcher with a text editor ("srcds_run"). There should be a line that look like this:
export LD_LIBRARY_PATH=bin:$LD_LIBRARY_PATH
Depending on the Linux distribution that you and you user choose (because not all Linux distributions agrees on the standards), you will have to add to the beginning the path to your system's "libstdc++.so.6". On Debian/Ubuntu IIRC, the path should be "/usr/lib/i386-linux-gnu", so the variable would look something like this:
export LD_LIBRARY_PATH=/usr/lib/i386-linux-gnu:bin:$LD_LIBRARY_PATH
Save the file, and it should pickup the "libstdc++.so.6" from your system.
Alternative: You could delete the "libstdc++.so.6" shipped with HLDS/SteamCMD. If it complains about missing file, you could make a symbolic link.