Ok. I found the solution. I write it here in case someone has the same problem.
For Redhat / CentOS / Fedora download this rpm (it's an updated version of libstdc++).
Put it in your ovftool directory where the other library files are.
Unpack it:
rpm2cpio libstdc++-4.4.0-4.i586.rpm | cpio -i --make-directories
Move the files unpacked to the directory of ovftool:
mv usr/lib/libstdc++.so.6* .
Now when you run the tool it will search the libraries needed first in its own directory and use them.
Cheers.