[Issue 20338] dmd, phobos, and druntime build systems should be updated

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=20338

--- Comment #2 from Alan.W.Irwin1234 at gmail.com ---
I forgot to mention another issue with your present build and test system is
the dmd test target cannot be built with the GNU make parallel build (-jN)
option.
So my script drops that possibility for dmd and phobos on the assumption that
the phobos build/test system has the same issue.  CMake provides a powerful
environment (for example, dependencies between tests) to solve such parallel
build issues.

Also, to expand on my remarks about different build systems for Posix (where
you currently use a Makefile approach) and Windows (where you currently appear
to have a build system that works for Visual Studio), CMake has different
generators which allow it, for example, to configure Posix Makefiles, a Visual
Studio project, and many other possibilities (such as nmake Makefiles).

However, I don't want to over-advocate CMake so I also want to emphasize this
parallel test issue, and all the other Posix build-system issues I have
mentioned could be addressed at the Makefile level and assuming the same or
similar issues exist for your Visual Studio build could also be addressed for
that build system.  Or maybe [Digger](https://github.com/CyberShadow/Digger)
(which I have not tried) is the answer.  But the fundamental point is all these
current build-system issues I have mentioned need to be addressed whatever
build system you decide to adopt.

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