Get bundled curl to be used on OS X too
Don't force "yes" on Darwin.

Change-Id: I3a6a2ecdf15325d07fb22b9a6bb0da7b313036cb
Reviewed-on: https://gerrit.libreoffice.org/7197
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>