Using GtK

[Ruby The Roobster]

I have a very basic program that does ABSOLUTELY NOTHING.  Here 
is the code:
```d
import gtk.Main;
import gtk.MainWindow;
import gtk.Widget;
void main()   {
}
```
I am using gdc version 10.3.0 on Ubuntu 20.04.  Assuming the file 
name is test.d, here is my command line:

gdc -I/usr/include/gtkd-3 -L-ldl -L-libgtkd-3 test.d

It generates the following errors:

/usr/bin/ld: /tmp/ccelqCb4.o:(.data.rel+0x10): undefined 
reference to `_D3gtk10MainWindow12__ModuleInfoZ'
/usr/bin/ld: /tmp/ccelqCb4.o:(.data.rel+0x18): undefined 
reference to `_D3gtk4Main12__ModuleInfoZ'
/usr/bin/ld: /tmp/ccelqCb4.o:(.data.rel+0x20): undefined 
reference to `_D3gtk6Widget12__ModuleInfoZ'
collect2: error: ld returned 1 exit status

Why is this, and how can I fix it?  Thanks in advance.