How to compile for Win64 with Visual D? Optlink error?

[Timothy Foster]

I'm trying to compile my project as a Win64 application but this 
is happening:

Building C:\Users\me\test\test.exe...
OPTLINK (R) for Win32  Release 8.00.17
Copyright (C) Digital Mars 1989-2013  All rights reserved.
http://www.digitalmars.com/ctg/optlink.html
OPTLINK : Warning 183: Extension not .RES : 
obj\debug\dummy\test\..\source\c.obj
obj\debug\dummy\test\..\source\b.obj(1) : Error 52: .DEF Syntax 
Error
d†š
öñÀY$@

^
Building C:\Users\me\test\test.exe failed!


I'm on a Win64 machine and compiling Win32 works fine. I'm using 
Visual Studio 17 Community with Visual D. DMD is up to date as is 
Visual D.

I added a x64 "solution platform" to the configuration manager 
which added a -m64 flag to my linker options. I'm not sure what 
else I'm meant to do to get it to compile as x64?