kbuild - the new Makefile

Old kbuild used multiple Makefiles
Harder to parallelize everything
Spurious rebuilds

Now, only a single, top-level Makefile exists
Built from Makefile.in fragments
Can slow down build at beginning
No unneeded rebuilds
(Almost) any mixture of targets works

To override Makefile regeneration:
make NO_MAKEFILE_GEN=1