Sorry I've taken a long time to reply. There is actually a libstdc++ version 4.9 package in Debian Jessie (Testing) here
. This is the reason why the package got compiled using libstdc++ version 4.9, as I run an up-to-date version of Debian Jessie 64-bit on my machine.
The packages are also hosted here
, where there are also source packages if you would like to put libstdc++ 4.8 on your package. The package will tell you what you need to compile it, and the compilation directions are in the repo. I cannot myself compile it with libstdc++ 4.8 because of technical reasons I will not get into here.