As we have previously written, both the Ubuntu and the Debian developers have decided to make GCC 5.x the default compiler on their future Linux systems.
While the Ubuntu Touch branch based on Ubuntu 15.10 already uses GCC 5, Debian Sid (currently Unstable) has also adopted GCC5.
This is Debian’s Matthias Klose announcement:
“Finally sid deserves its name again. GCC 5 is now the default in unstable and packages for the follow-up transitions are (and can be) uploaded to unstable. Thanks for getting to the point where we could make GCC 5 the default, fixing hundreds of issues, thanks to package maintainers fixing issues them self, to David Suarez for test rebuilds, to our NMU machine gun Gregor Herrmann, to the kind people of HP organized by Martin Michlmayer, and anybody else helping with these fixes,”
Changing default compiler is a little problematic because the packagers need to verify that the new changes are compatible with the new version of GCC.