command line option or other method for determining the front end version of gdc

[dan via D.gnu]

One of my machines (running ubuntu mate 16.04) did some update 
and gdc is no longer able to compile a library that i like to use 
(gtkd).

So i want to build a gdc using an earlier front-end to avoid the 
problem.

However, i don't know what front end is compiled into gdc, so i'm 
unclear on which front-end to try get an earlier version of.

If i run the command
     gdc --version
it gives me the gcc version.

The command
     gdc --verbose --version
gives a lot more information, but i can't tell the front end 
version from that either.

Even running commands like
     strings /usr/bin/gdc | grep .....
doesn't seem to reveal the version.  (I think the version is 
probably 2.06* but '2.06' and '206' do not appear in the strings.)

Nevertheless i'm sure the information must be there.

TIA for any info!