autotools: no commit hash in ceph_ver.h when working on sources

Having the commit hash in ceph_ver.h triggers too many compilations
because the erasure code plugins depend on them. Worst case it triggers
a version mismatch when only part of the tree is recompiled.

Instead create a fixed ceph_ver.h when ./do_autogen.sh -d 1 or greater
is used or when the --without-commit-hash configure flag is set.

http://tracker.ceph.com/issues/9413 Fixes: #9413

Signed-off-by: Loic Dachary <loic-201408@dachary.org>