automake: rework the git_sha1.h rule, include in tarball

As we'll need the file in the release tarball, rework the rule so that
the file is regenerated _only_ if we're in a git repository.

With this in place we can build vulkan (anv) from a release tarball.

Cc: Jason Ekstrand <jason.ekstrand@intel.com>
Cc: Kristian Høgsberg Kristensen <krh@bitplanet.net>
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
2 files changed