Buildroot:2016.02

Remaining things to merge before 2016.02-rc1:


 * Bump of ARC toolchain to 2015.12, so that when the external Buildroot toolchains will be rebuilt, we'll use the newer ARC tools
 * The atomic series, since it fixes a number of build failures, and will allow to fix more of them
 * Gtk2/Gtk3 circular dependency fixes from Yann.

Needed for 2016.02, but can wait after -rc1:


 * The patch series clarifying the licensing of the patches
 * As many musl build fixes as possible