Create a new project branch, release-noxdev, for
a sandbox workspace outside of head/ to update the
release bits for arm builds since the deprecation of
the XDEV and XDEV_ARCH make(1) variables.

Define load_chroot_env() and load_target_env()
prototypes.

Call load_chroot_env() and load_target_env() where
they can be mutually conflicting with regard to
TARGET, TARGET_ARCH, XDEV, and XDEV_ARCH.

Add shebang line to arm/*.conf files since these
should be considered to be executable (albeit not
on their own) shell scripts.

Redefine load_chroot_env() and load_target_env() in
the arm/*.conf files, and reindent.

Simplify where load_chroot_env() and load_target_env() are
called.

Provide example in release.conf.sample for overriding the
load_chroot_env() and load_target_env() prototypes.

Remove a gratuitous newline.

Unset potentially conflicting variables in load_chroot_env()
and load_target_env().

Make global variables global, and accessible outside of
the functions within which they were once defined.

Remove XDEV/XDEV_ARCH evaluation if EMBEDDEDBUILD is set.

In arm/release.sh, switch TARGET/TARGET_ARCH back to the
original XDEV/XDEV_ARCH make(1) variables.

In theory, this should have been a no-op, but the TARGET and
TARGET_ARCH are now unset in load_target_env() to avoid
collision with the chroot userland.

Export variables in the arm/*.conf files because they
need to be passed through release.sh to arm/release.sh.

Set MK_TESTS=no for the xdev target.

As part of the XDEV/XDEV_ARCH deprecation, the
'xdev-links' target was intentionally no longer
invoked automatically.

Invoke the xdev-links target after xdev, which
creates, for example, /usr/bin/armv6-freebsd-cc
symlink to /usr/armv6-freebsd/usr/bin/cc.

Set TARGET and TARGET_ARCH to the XDEV and XDEV_ARCH
counterparts for the xdev and xdev-links make(1)
targets.