The next Ubuntu LTS release (16.04 LTS) will use GCC 5 as the standard compiler (and likely GCC 6 as the standard for go). We do not want to change the default compiler during the six months leading to the LTS, so we will make the switch to GCC 5 for 15.10.

Besides fixing the usual build failures (around 350), GCC 5 introduces an new libstdc++ ABI which makes it difficult to combine code built with the new and the old ABI. The ABI break is not in libstdc++ itself, but then in libraries using the libstdc++ ABI.