Add support for host32 for DIRDEPS_BUILD

Allow building 32bit libs for host.

Move CFLAGS additions from local.sys.dirdeps.mk (which is too early
and impacts CFLAGS defaults) to local.sys.mk

Reviewed by: stevek
Sponsored by: Juniper Networks, Inc.
Differential Revision: https://reviews.freebsd.org/D41946

Remove $FreeBSD$: one-line sh pattern

Remove /^\s*#[#!]?\s*\$FreeBSD\$.*$\n/

Simplify building host tools during DIRDEPS_BUILD

The whole point of the DIRDEPS_BUILD is to avoid tree walks
and basically build everything in a single pass.
We use the pseudo MACHINE "host" to represent the build host.

When the build host is not FreeBSD or is an older version of FreeBSD
it may need some help to build host-tools.

The directory tools/build does this - building libegacy.

local.sys.mk: create a pseudo option MK_host_egacy to indicate
if tools/build needs to be built for "host".

local.dirdeps.mk: set MK_host_egacy.host to ${MK_host_egacy}
all other DEP_MACHINES will get "no"

This allows a Makefile.depend.options in makefs etc to cause tools/build
to be built for host but only if necessary.

local.init.mk: use ISYSTEM as arg to -isystem so that it can be overridden.
The default remains ${STAGE_INCLUDEDIR}

src.init.mk: if MACHINE is host and we are not FreeBSD
set some MK_ flags the same as tools/build/mk/Makefile.boot.pre and
include src.init.${.MAKE.OS:tl}.mk if it exists.

For older versions of FreeBSD add libegacy when building PROGs for "host"

Also instead of -isystem${STAGE_INCLUDEDIR} we want
-I${STAGE_INCLUDEDIR} and -isystem/usr/include so we override ISYSTEM.
This means any headers we stage for "host" will take precedence over
system headers but #include_next will DTRT.

src.init.linux.mk: add
-I${SRCTOP}/tools/build/cross-build/include/linux
and generally deal with building host tools on Linux.
Eg. static linking does not work so set NO_SHARED= no
Override some HAVE_ flags.

src.sys.env.mk: on linux awk throws an warning about # in newvers.sh
just send stderr to /dev/null

Reviewed by: jrtc27, arichardson
Sponsored by: Juniper Networks, Inc.
Differential Revision: https://reviews.freebsd.org/D39744

Allow site.*.mk to augment local.*.mk and src.*.mk

Add some extra customization points so that FreeBSD build
can be adapted to local requirements.
We use these to minimize changes to share/mk

Reviewed by: stevek
Sponsored by: Juniper Networks, Inc.
Differential Revision: https://reviews.freebsd.org/D37617

Include ${.CURDIR}/local.init.mk if it exists

This is handy for making local hacks to an app
(eg to build it as tool for non-BSD host)
without making a mess of the code base.

Reviewed by: bdrewery
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org//D24101

Define .MAKE.MODE to normal to avoid the need for :U later.

Sponsored by: EMC / Isilon Storage Division

META MODE: Fix MACHINE=host builds.

We need to not use -nostdinc since it breaks building of clang itself. Use
-isystem rather than -I/usr/include and -nostdinc which gets us using
the stage include directory before searching the real host headers.
This allows removing more of the -I hacks to get host headers since the
headers are no longer excluded. The -B seemed unneeded.

This fixes building of secure/lib/libcrypto which was looking at the
/usr/include/openssl/asn1.h header rather than the staged one.

This fixes building of clang which wants to find its own internal
headers in the STAGEDIR/usr/lib/clang/* path.

Sponsored by: EMC / Isilon Storage Division

Move META MODE's HOST_CC/CXX/CPP setting to local.meta.sys.mk, which
centralizes the handling of CC and HOST_CC.

This fixes a bug with WITH_CCACHE_BUILD when using MACHINE=host since
CC is overridden in local.init.mk via src.opts.mk long before bsd.compiler.mk
is included.

Originally the ccache implementation was placed in local.init.mk but moved
to bsd.compiler.mk as it seemed more proper and avoided other ordering
issues.

Sponsored by: EMC / Isilon Storage Division

Allow 'make buildenv' to work anywhere in the src tree.

Sponsored by: EMC / Isilon Storage Division

Do not assume host toolchain supports sysroot

META_MODE: Set HOST_CXX and HOST_CPP and chain them down into CXX/CPP for host builds.

Sponsored by: EMC / Isilon Storage Division

do not include src.opts.mk from here

Building on fmake is no longer possible so removed tests for bmake.

Move META_MODE bits to local.meta.sys.mk

By moving META_MODE bits from local.sys.mk, they are easier
to skip when MK_META_MODE=no

Update some filters to cope with sync from head.

If buildworld etc or WITHOUT_META_MODE disable all the META_MODE
related options.

Include src.opts.mk and handle MK_SYSROOT.

Sync FreeBSD's bmake branch with Juniper's internal bmake branch.

Requested by: Simon Gerraty <sjg@juniper.net>