How to setup GDC with Visual D?

[Marko Grdinic via Digitalmars-d-learn]

DMC works fine, but when I try to compile using GDC it seems it 
can't find the compiler:

Building Release GDC x64\ConsoleApp1.exe...
failed launching gdc -m64 -O3 -frelease "-fXf=Release GDC 
x64\ConsoleApp1.json" "-fdeps=Release GDC x64\ConsoleApp1.dep" -o 
"Release GDC x64\ConsoleApp1.exe" main.d
Building Release GDC x64\ConsoleApp1.exe failed!

I've tried setting the GDC directory to different levels in the 
tree, but it gives me the same error regardless. I haven't tried 
adding GDC binaries to the PATH yet, but I am not sure whether I 
should. I am (trying) to use the latest unsupported alpha build 
because the supported version in from 2013 and so I am unsure 
whether I should use it.

I only dabbled in D a few months ago when I was writing the 
compiler project for the online course, but did not study it 
much. Lately though, I've been trying to solve a tough problem on 
CodeChef and F# is 4x slower than the C++ version on the online 
judge which makes all my solutions time out. It would have been 
fine had it been only 2x just as it is on my machine locally.

At any rate, as I've acquired the functional programming style 
recently, I do not want to go back to writing C++ unless I am 
forced to and I know GDC can match it in speed based on what I've 
read on the web.

Any advice regarding how I can get this to work? Thanks.