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

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

Add META_MODE support.

Off by default, build behaves normally.
WITH_META_MODE we get auto objdir creation, the ability to
start build from anywhere in the tree.

Still need to add real targets under targets/ to build packages.

Differential Revision: D2796
Reviewed by: brooks imp