dlang.org/posix.mak dependencies

[Borden]

Good evening, all,

I'm making a new thread on this because my question isn't 
strictly related to the DDoc issues I've mentioned in earlier 
threads. Rather, it has to do with the dependencies of the 
posix.mak file in the dlang.org repo (on GitHub, for greater 
clarity):

posix.mak, beginning at line 236, compiles local copies of DMD, 
DRuntime and Phobos. Is all of this extra compilation really 
necessary for someone who, presumably, already installed D using 
the installer packages?

Wouldn't it be more reasonable to see if the most current version 
of DMD is installed and, if not, panic out and tell the user to 
go and fetch the latest copy from the website? Then the rest of 
the makefile could use the installed copies on the user's 
computer rather than download and recompile them?

This question is specific to the dlang.org repo and NOT to any 
other repos hosted at GitHub.