Problem reported by Michael Brand in:
http://lists.gnu.org/archive/html/emacs-devel/2016-05/msg00367.html
* autogen.sh (git_config): Don't assume that git rev-parse
groks --git-common-dir.
# Get location of Git's common configuration directory. For older Git
# versions this is just '.git'. Newer Git versions support worktrees.
-test -e .git && git_common_dir=`git rev-parse --git-common-dir 2>/dev/null` ||
- git_common_dir=.git
+{ test -e .git &&
+ git_common_dir=`git rev-parse --no-flags --git-common-dir 2>/dev/null` &&
+ test -n "$git_common_dir"
+} || git_common_dir=.git
hooks=$git_common_dir/hooks
# Check hashes when transferring objects among repositories.