Lots of useful build targets are listed at the top of the Makefile
When hacking on DDC we usually use the the bin/ddc target to avoid dependency checking the runtime system and external libs each time around.
$ make bin/ddc
The build can be tweaked by creating the file make/config-override.deps. Note that you don't want to change make/config.mk directly because this file is under version control.
The make/config.mk file lists a number of additional build flavours. For the fastest build add the following line to make/config-override.deps.
BUILDFLAVOUR = devel
This turns off some GHC optimisations, and reduces the amount of rebuilding that must be done after changing one of the compiler source files.
The makefile is set up to use the value of the THREADS variable wherever possible.
The default is currently 2, but if you have more then override it with something like:
THREADS = 8 # or whatever