Normally, when a header file is removed from the build (as i4b headers
were recently), a simple 'make cleandepend; make depend' is sufficient
to keep the tree buildable after a cvs update when doing incremental
builds.

However, kdump and truss use a script which searches for header files
that define ioctls, and generates C code that includes them. This
script will usually not need updating when a header file is removed,
so the normal dependency mechanism will not realize that it needs to
be re-run. One is therefore left with code that references dead files
but will only be removed by a full 'make clean', which defeats the
purpose of incremental builds.

To work around this, modify the cleandepend target in bsd.dep.mk to
also remove any files listed in a new variable named CLEANDEPFILES,
and modify kdump's and truss's Makefiles accordingly.

MFC after: 2 weeks