adapt to ${CC_WNO_IMPLICIT_FALLTHROUGH}

Use ${CC_WNO_IMPLICIT_FALLTHROUGH} instead of
the older style more complex expressions.

bsd.own.mk: rename to CC_WNO_ADDRESS_OF_PACKED_MEMBER

Provide a single variable
CC_WNO_ADDRESS_OF_PACKED_MEMBER
with options for both clang and gcc, to replace
CLANG_NO_ADDR_OF_PACKED_MEMBER
CC_NO_ADDR_OF_PACKED_MEMBER
GCC_NO_ADDR_OF_PACKED_MEMBER

Using the convention CC_compilerflag, where compilerflag
is based on the full compiler flag name.

bsd.own.mk: rename NO_ADDR_OF_PACKED_MEMBER to CC_NO_ADDR_OF_PACKED_MEMBER

Add "CC_" prefix to NO_ADDR_OF_PACKED_MEMBER.

We now have the following convention:
GCC_NO_*: Disable specific warnings from GCC.
CLANG_NO_*: Disable specific warnings from Clang.
CC_NO_*: Disable specific warnings from both Clang and GCC.

This reserves "NO_*" Makefile variables to disable other features.

Some space->tab fixes.

Provide a global no-packed-address for both gcc and clang

use the GCC_ warning variable

Avoid alignment of packed member

convert HAVE_GCC == 7 to HAVE_GCC >= 7.

Bump default value of WARNS for modules from 3 to 5, and
explicitly set WARNS for modules that fail with WARNS=5.

Also, turn on -Wno-missing-noreturn for clang for some files.

At the moment, among ~ 360 modules,
- 2 (lua and zfs) need WARNS=0
- 1 (solaris) needs WARNS=1
- 136 need WARNS=3 (mostly due to sign-compare)
- 4 need WARNS=4
- others can be compiled with WARNS=5

Discussed on tech-kern.

- use -Wno-error=implicit-fallthrough with GCC7.

branches: 1.9.4;
Code is fixed, so hiding the warning is not necessary any more.

Simplify and make the GCC check more precise at the same time.

Fix building with MKGCC=no

Avoid gcc 6 specific options when compiling with gcc 5

pf_table.c has many left-shift of negative value issues.

Add ioconf entries to the pseudo-devices.

branches: 1.3.12; 1.3.30;
build pf module with WARNS=3, and remove the need for -Wno-shadow

set default WARNS for modules to 3 -- the only one that needs < 3 now is pf

branches: 1.1.2; 1.1.4; 1.1.6;
Add new type kernel module for pf (includes pflog, but not pfsync).

Remove bpfilter.h as not needed.

Add new type kernel module for pf (includes pflog, but not pfsync).

branches: 1.1.2; 1.1.4; 1.1.6;
Add new type kernel module for pf (includes pflog, but not pfsync).

branches: 1.1.2; 1.1.18;
Add ioconf entries to the pseudo-devices.

branches: 1.1.2; 1.1.4; 1.1.6;
Add new type kernel module for pf (includes pflog, but not pfsync).

branches: 1.1.2; 1.1.4; 1.1.6;
Add new type kernel module for pf (includes pflog, but not pfsync).