I use an embedded with a bit old kernel 2.6.37.
Now we need to update
rootfs with more update
gcc than the one used on building the image (Instead of 4.3 need to use 5.1, because it will support c++11, which we need in application).
I thought to do it using latest buildroot for this and use it with linaro toolchain 5.1.
It first compliant (in buildroot make) that there is mismatch between kernel header 2.6.x (which I gave as toolchain configuration for buildroot) because it detects that the external toolchain I've configured is using kernel headers 4.0.0.
The thing is that I don't use any kernel modules, so I think that there is no issue in such case if there is mismatch between kernel and kernel headers. Is that correct ?