databases/libgda2 fails to link with WITH_FIREBIRD

[John Merryweather Cooper]

I have databases/firebird installed which causes WITH_FIREBIRD to be set 
by default in databases/libgda2.  Everything compiles fine, but when the 
link stage is reached, the build bombs complaining that it can't find 
libdl.  A "-ldl" flag is being passed on the command line.  The only 
libdl I can find on my system is in /usr/compat/linux/lib (which I'm 
pretty sure wouldn't work as expected).

jmc