I'm new to D so I'm not sure this is the best solution, but I was not able to build with gdc 4.8.1 on Kubuntu 13.10 x86_64 before these changes, and I am able to afterwards.
$ gdc --version
gdc (Ubuntu/Linaro 4.8.1-10ubuntu8) 4.8.1
Copyright (C) 2013 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
update gdc compile flags
create output directories before writing .o files