The kernel and the C library as a single project

Sure single project mentality helps big time in actually designing the right solution. But why does that require a single 'module'? Is it impossible to post two different to two different patches to two different projects, in this case linux/glibc ?

It seem possible in gnome where each module is seperate git repo, or some lower system parts has added a feature that should be propogated upwards. But people manage to 'cross-patch'.

Or does current tools suck when handling two seperate projects?