docs: Kbuild/Makefile: allow check for missing docs at build time

While this doesn't make sense for production Kernels, in order to
avoid regressions when documents are touched, let's add a
check target at the make file.

Signed-off-by: Mauro Carvalho Chehab <[email protected]>
Signed-off-by: Jonathan Corbet <[email protected]>
4 files changed