For dmd you use build.d that is in the repository. For phobos win64.mak (used for 32bit by default as well):
"# Makefile to build D runtime library phobos{64,32mscoff}.lib for Windows MSVC"
So MSVC make.Beyond that idk, but its starting point (oh and druntime is now in dmd repo, so ugh... yeah)
