bsd.own.mk: rename GCC_NO_* to CC_WNO_*

Rename compiler-warning-disable variables from
GCC_NO_warning
to
CC_WNO_warning
where warning is the full warning name as used by the compiler.

GCC_NO_IMPLICIT_FALLTHRU is CC_WNO_IMPLICIT_FALLTHROUGH

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

introduce some common variables for use in GCC warning disables:

GCC_NO_FORMAT_TRUNCATION -Wno-format-truncation (GCC 7/8)
GCC_NO_STRINGOP_TRUNCATION -Wno-stringop-truncation (GCC 8)
GCC_NO_STRINGOP_OVERFLOW -Wno-stringop-overflow (GCC 8)
GCC_NO_CAST_FUNCTION_TYPE -Wno-cast-function-type (GCC 8)

use these to turn off warnings for most GCC-8 complaints. many
of these are false positives, most of the real bugs are already
commited, or are yet to come.


we plan to introduce versions of (some?) of these that use the
"-Wno-error=" form, which still displays the warnings but does
not make it an error, and all of the above will be re-considered
as either being "fix me" (warning still displayed) or "warning
is wrong."

branches: 1.4.98;
Implement MKDYNAMICROOT, which currently defaults to "no", but will
be changed in the future to "yes".

If MKDYNAMICROOT == "no", there is no change from existing behaviour
of a static /bin and /sbin (and a few programs in elsewhere).

If MKDYNAMICROOT == "yes", the following changes occur:
in <bsd.own.mk>:
SHLIBDIR?= /lib
SHLINKDIR?= /lib
in various Makefiles, the following entry is DISABLED.
LDSTATIC?=-static
This results in all programs (except those "standalone" programs built
in sys/arch/*/stand) are linked dynamically, the shared linker is moved
from /usr/libexec to /lib (with a compat symlink), and the shared
libraries used by /bin and /sbin programs are moved from /usr/lib to
/lib (with compat symlinks).

as this installs in /sbin, set LDSTATIC?=-static. fixes PR [bin/14886]

Put tbrconfig(8) into /sbin so it's usable during early
setup, and can be executed from ifconfig.xxx.

Build glue for ALTQ programs.