OpenSSL @OS X: choose correct build target

Change-Id: I58f3cc12f2fa177c26608d372f99c086503a13a5
Reviewed-on: https://gerrit.libreoffice.org/8205
Reviewed-by: Norbert Thiebaud <nthiebaud@gmail.com>
Tested-by: Norbert Thiebaud <nthiebaud@gmail.com>