Fix: git -C not available for git 1.8

Fix: git -C not available for git 1.8

Our deploy slaves are running CentOS, which only has git 1.8.3.
git -C option was made available in git 1.8.5, so instead of
installing out of repo versions of git on all our deploy slaves,
rework the main Armband Makefile to NOT use this option.

NOTE: --git-dir could be used instead, too.

Change-Id: I29b9c720e39cae25431cf1176dbaddce5bda2a35
Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>