MFC r314651,r318439,r318440:

r314651:

sys/modules: normalize .CURDIR-relative paths to SRCTOP

This simplifies make output/logic

Tested with: `cd sys/modules; make ALL_MODULES=` on amd64

r318439:

Normalize .PATH on SRCTOP

This will help Jenkins dedupe 9 warnings between the static build and
the module build of ipsec(4).

Missed in SRCTOP conversion in r314651.

MFC with: r314651

r318440:

Normalize SYSDIR on SRCTOP instead of .CURDIR

This is being done to simplify pathing for CFLAGS and source files.

Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Move most of the 15 variations on generating opt_inet.h and
opt_inet6.h into kmod.mk by forcing almost everybody to eat the same
dogfood. While at it, consolidate the opt_bpf.h and opt_mroute.h
targets here too.

Per email to arch@ a little while ago (that was greeted with silence),
prefer the more common > ${.TARGET} over > opt_foo.h in modules
makefiles.

Fix our ioctl(2) implementation when the argument is "int". New
ioctls passing integer arguments should use the _IOWINT() macro.
This fixes a lot of ioctl's not working on sparc64, most notable
being keyboard/syscons ioctls.

Full ABI compatibility is provided, with the bonus of fixing the
handling of old ioctls on sparc64.

Reviewed by: bde (with contributions)
Tested by: emax, marius
MFC after: 1 week

Let modules use the kernel's opt_*.h files if built along with
the kernel by wrapping all targets for fake opt_*.h files in
.if defined(KERNBUILDDIR). Thus, such fake files won't be
created at all if modules are built with the kernel.

Some modules undergo cleanup like removing unused or unneeded
options or .h files, without which they wouldn't build this way
or the other.

Reviewed by: ru
Tested by: no binary changes in modules built alone
Tested on: i386 sparc64 amd64

Mechanically tidy up the contents of CLEANFILES:M*.h: kmod.mk
automatically removes opt_*.h and if_*.h found in SRCS.

Use a consistent style and one much closer to the rest of /usr/src

Avoid the modules madness I inadvertently introduced by making the
cloning infrastructure standard in kern_conf. Modules are now
the same with or without devfs support.

If you need to detect if devfs is present, in modules or elsewhere,
check the integer variable "devfs_present".

This happily removes an ugly hack from kern/vfs_conf.c.

This forces a rename of the eventhandler and the standard clone
helper function.

Include <sys/eventhandler.h> in <sys/conf.h>: it's a helper #include
like <sys/queue.h>

Remove all #includes of opt_devfs.h they no longer matter.

Somehow the module makefile got missed in the big commit.