RFR: Improve and modernize the makefile

[Jesper Wilhelmsson]

On Mon, 15 Mar 2021 16:24:05 GMT, Magnus Ihse Bursie <ihse at openjdk.org> wrote:

>> A bunch of fixes to the make file, to use more modern/robust syntax, and to keep intermediate build results.
>> 
>> This is a prerequisite for any further changes to the make file.
>
> Note that with this change, the build result end up in `build/dist`, rather than `build` directly. Deployment scripts will likely need adaption to this change. 
> 
> The new directory `build/support` contains intermediate results that are needed by the build.

I don't mind this change but I think it may be slightly premature as the chapters aren't nearly as stable as one might think :-)
The GIT rewrite will change things a lot. I would prefer to hold this change until that's done.

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PR: https://git.openjdk.java.net/guide/pull/46