[Libreoffice] PostgreSQL-SDBC: enable by default on GNU/Linux, BSD

Hi,

So, PostgreSQL-SDBC is now in libreoffice master branch, but not
enabled by default. Let's enable it by default on "traditional" Unices
(GNU/Linux, BSD, but not MacOS X yet), where we have a working
internal libpq (PostgreSQL C client library), so no extra build
dependency.

I would be nice if tinderboxes for these platforms (i.e. only
GNU/Linux AFAIK) would build it too, to get a bit more test coverage
than my Debian box :) Do the tinderboxes just use distro-config/FOO or
does this need manual intervention by the tinderbox operators? If
enabling it breaks the tinderbox build (on a traditional Unix), warn
me, I'll take care of it.

-- 
Lionel