[Libreoffice] gbuild'ified salhelper

<http://cgit.freedesktop.org/libreoffice/core/commit/?id=a4312af08cbd8c69ba4bead9608f3bf549caf7a0> 
converts salhelper to gbuild directly on master (rather than on 
feature/gbuild branch, should help us find out faster if it breaks on 
some platform).  Technically its the earliest feature/gbuild-changeset 
cherry-picked, plus additional modifications to keep salhelper backwards 
compatible.  See the commit message for details.

I tried this on Linux and Mac OS X, and I *think* it should not break 
anything on Windows (fingers crossed).  At least on Mac, the resulting 
salhelper library is substantially larger than the old dmake-based one, 
I'm investigating that.

Björn, Michael, some of those changes are rather bad hacks, maybe one of 
you can add some gbuild magic to improve them to something acceptable.

Stephan