[Issue 18550] Offline option for dlang.org makefile

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=18550

--- Comment #4 from hsteoh at quickfur.ath.cx ---
Argh, is there a way to tell the `phobos-prerelease` target to just use the
local dmd repo instead of yet another remote cloning?

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