[BUILD] use "git cmd" instead of "git-cmd"

[BUILD] use "git cmd" instead of "git-cmd"

Newer GIT versions do not support "git-cmd" anymore, so date and version
can be wrong during development builds. Use "git cmd" now. Also fix
git-tar to use "git archive" instead of "git-tar-tree".
(cherry picked from commit 63076b3f611803a9bf9e6012193f89d14ccc32d2)

[wt: finally decided to merge it into 1.3.15.x because packaging
 backports was becoming an annoying experience].
(cherry picked from commit e68f64fd01d5c4fd561a82642f112bd5376bb8df)