Produce vala debug information
Build with 'valac -g' to make sure we have good vala debug information.
gnome-contacts has a history of crashing fairly often so it's important
to get good backtraces to be able to work with upstream.
Most (all?) of the debug info is just going to get split out into
-debuginfo and -debugsource subpackages, so it shouldn't affect runtime
much, if at all.