Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

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

MFC r262810, r262862, r264105, r264107:

r262810:
Merge enabling building FreeBSD/arm images as part of the
release build process.

r262862:
Provide backwards-compatibility with release.conf SVNROOT
entries that do not have a trailing '/'.

r264105:
Add ZEDBOARD support for release builds.

r264107:
Remove only-works-on-amd64 restriction.

* Local modifications to stable/9:
- Set SRCBRANCH from head/ to stable/9/.

Sponsored by: The FreeBSD Foundation

Merge ^/projects/release-embedded into ^/head.

After several months of testing and fixing (and breaking)
various parts of release/release.sh changes, it is now
possible to build FreeBSD/arm images as part of the release
process.

When EMBEDDEDBUILD is set in the release.conf file, release.sh
will create the build environment, then run a separate script
in release/${XDEV}/release.sh [1]. Currently, only arm is
supported.

The release/${XDEV}/release.sh configures the build environment
specific for the target image, such as installing gcc(1),
installing additional third-party software from the ports tree,
and fetching external sources.

Once the build environment is set up, release/${XDEV}/release.sh
runs Crochet, written by Tim Kientzle, which builds the userland
and kernel, and creates an image that can be written to an SD
card with dd(1). Many thanks to Tim for his work on Crochet.

Sample configurations for FreeBSD/arm boards are in the
release/arm/ directory, and Crochet configuration files for each
board are located in release/tools/arm/. Supported boards at this
time are: BEAGLEBONE, PANDABOARD, RPI-B, and WANDBOARD-QUAD.

Adding support for additional boards will continue in the
projects/release-embedded/ branch, and incrementally merged back
to head/.

Many thanks to the FreeBSD Foundation for the support and
sponsorship of this project.

[1] XDEV is used in order to keep the various configurations
organized by architecture, but since TARGET and TARGET_ARCH
are used to build the chroot, the values of those variables
cannot be used.

MFC after: 1 month
Sponsored by: The FreeBSD Foundation

Merge the following:
^/user/gjb/hacking/release-embedded:
259994,260000,260895-260896,261139,261152,
261174,261176,261210,261221,261237,261239,
261448,261489
^/user/gjb/release-embedded:
262305,262307

svn:mergeinfo is intentionally not included in the commit, so it does
not propagate to head/.

Sponsored by: The FreeBSD Foundation

Move tools/release/${XDEV}/ to release/tools/${XDEV}/.

In general, the workflow used for the latest releases has been
to checkout head/release/ to a directory outside of any build
environments, modify the release.conf accordingly, and run:

# ./release.sh -c ./release.conf

By moving tools/release/${XDEV}/ (for RPI-B build testing, in
this case), any dependency on a different branch of the source
tree can be removed. In particular, release.sh expects the
tools/release/${XDEV}/crochet-${KERNEL}.conf file to exist, so
by moving the crochet configuration file to a directory in
release/, it becomes possible to build images for branches that
do not yet have the necessary configuration files and/or scripts.

Sponsored by: The FreeBSD Foundation