Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

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

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

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

Fix comma splice, can't ambiguity and quoting.

Submitted by: bde@
MFC after: 2 weeks

Wordsmith the can't find kernel error message, and suggest which
variable to set to override.

ata module additions now nest ata modules one deeper than any prior module.
Increase heuristic used to find them by one.

Fixed style bugs in previous commit (151 characters of trailing whitespace).

- Missing trailing slash for a kern directory check.
- Check in both places if ${_dir}/conf/kmod.mk exists.
- Style fixes (lines too long).

Submitted by: bde

Check if ${_dir}/kern exists as well, because if it doesn't exists
we will fail later and we can miss good kernel source tree directory.
I found this trying to compile kld module and it finds 'conf/kmod.mk'
in '../..', but it fails later, because there is no 'kern' directory,
but there is valid kernel source tree still in /usr/src/sys/.

(Previous commit was made prematurely before I could finish composing
the log message)

Bring in the WARNS directive from NetBSD, localized in a new bsd.sys.mk
to avoid polluting sys.mk. This directive controls the addition of
compiler warning flags to CFLAGS in a relatively compiler-neutral manner.

The idea is that WARNS can be set in Makefile.inc or in individual
Makefiles as they become clean, to prevent the introduction of new
warnings in the code (-Werror is added by default when WARNS > 0).

This behaviour can be overridden with the following two knobs:
NO_WARNS disables the checking of WARNS completely
NO_WERROR disables the addition of -Werror to the flags.

Additionally, setting WFORMAT to 1 (in makefiles) and/or defining
FORMAT_AUDIT (by the user) will enable increased checking of format
string arguments.

Obtained from: NetBSD
Reviewed by: peter

Bring in the WARNS directive from NetBSD, localized in a new bsd.sys.mk
to avoid polluting sys.mk. This directive controls the addition of
compiler warning flags to CFLAGS in a relatively compiler-neutral manner.

The idea is that WARNS can be set in Makefile.inc or in individual
Makefiles as they become clean, to prevent the introduction of new
warnings in the code. -Werror is added by default

Do not check for existence of ${_dir}/kern/ , because for modules that set
.PATH to ${.CURDIR}/[...]/kern , the "exists" expression will fail for the
form exists(${.CURDIR}/[...]/kern/). This appears to be happening because
make is searching for the argument to "exists" by using .PATH rather than a
relative search, because .PATH and the argument match at the beginning.
Additionally, make appears to consider a path that starts with ${.CURDIR}
as relative, even though it expands to an absolute path.

The reason that most people aren't seeing this problem is that the absolute
paths of /usr/src/sys and /sys are also searched, so as long as the kernel
source can be found in at least one of those places, no problems surface.
This problem was inadvertently introduced on 1 December 2000, with the
addition of the sysvipc modules.

Add ${.CURDIR}/../../../.. to the list of places we look for the
kernel. The new moudles/sound/drivers/foo pushes us down one more
level.

Sigh. Use the correct path to bsd.conf.mk. It's times like this that I
regret giving up coffee.

Revive a skeleton for bsd.kmod.mk (which will be in the make search path)
that merely locates and includes sys/conf/kmod.mk.