Mac OS X 10.5 doesn't come with a dedicated sha1sum, but has make 3.81.
Allow openssl as alternative for the makefile, after all it isn't sha1
that matters. (also XCode's make is not affected by that specific bug)

Change-Id: Id212fca588980f7e151120cdfe281f7b5d8ac5a4
Reviewed-on: https://gerrit.libreoffice.org/2804Reviewed-by: Fridrich Strba <fridrich@documentfoundation.org>
Tested-by: Fridrich Strba <fridrich@documentfoundation.org>