Getting a development dmd tree going

[Andrei Alexandrescu]

I tried to update my dmd installation on a OSX machine due to 
https://issues.dlang.org/show_bug.cgi?id=20019. Sadly I reached an impasse.

First I tried to do what worked in the past - git rebase everything then 
build dmd with AUTO_BOOTSTRAP=1, then druntime, then phobos, then tools. 
That didn't work for reasons I mentioned in a couple of comments at 
https://issues.dlang.org/show_bug.cgi?id=20019.

Then I thought I'd fall back to a more basic procedure, listed in 
https://wiki.dlang.org/Starting_as_a_Contributor:

wget https://raw.githubusercontent.com/dlang/tools/master/setup.sh
bash setup.sh

That failed, too, apparently because building dmd first requires a 
preexisting copy of dmd to build build.d. The setup procedure does not 
cover that case.

So, shouldn't the procedure for getting D set up from scratch Just Work(tm)?

Thanks!