Redefine the removed __dev* for now

The __dev* directives and functions were removed in 3.8, as they
are no-ops. We still have use of them for older versions, thus
we should define them (as noops) if they don't exist.

Signed-off-by: Tzafrir Cohen <tzafrir.cohen@xorcom.com>
build_tools/make_version: If making from a tag show only the tag in the version.

Also, if there is no other version information use the directory name. Downloads
from gitweb will include the sha information in the build and otherwise a user
could locate the source directory via the embedded version information. I
believe this is better than an empty string.

Signed-off-by: Shaun Ruffell <sruffell@digium.com>
(cherry picked from commit 37371f19e97e5af645082fcafa42d9e18ef574e5)