One thing that would be useful was if you could set the $PATH to gdmd,
and some optional arguments to pass to it globally at the config top ? (say for instance for gdc-posix-tango)
I wasn't really sure if you could do it already with rebuild 0.18, so I just search/replaced:
[compile]
cmd=/opt/gdc/bin/gdmd -arch ppc -arch i386 -version=Posix -version=Tango -c $i
...
[link]
cmd=/opt/gdc/bin/gdmd -arch ppc -arch i386 $i -of$o
...
[shliblink]
shlibs=yes
cmd=/opt/gdc/bin/gdmd -arch ppc -arch i386 -q,-shared -q,-nodefaultlibs $i -of$o
...
[dyliblink]
dylibs=yes
cmd=/opt/gdc/bin/gdmd -arch ppc -arch i386 -q,-shared -q,-nodefaultlibs $i $l/dymoduleinit.d -of$o
...
Here I used an alternative prefix to gdc of "/opt/gdc",
and added flags for building Mac OS X Universal Binaries.