For various testing purposes, I started keeping both 32-bit and 64-bit versions of druntime/phobos around. However, I don't know how to tell dmd to look for the appropriate path depending on whether -m32 or -m64 was specified; the only way I've managed to get this to work was to specify in dmd.conf paths to both generated/linux/release/32 and generated/linux/release/64, but this causes spurious warnings during link time about one or the other libphobos.a being skipped due to incompatible architecture.
Why doesn't dmd just take the base path and automatically search the 32/64 bit subdirectories for libphobos.a? Or how do I coax it to do so? T -- Be in denial for long enough, and one day you'll deny yourself of things you wish you hadn't.